Particulate materials

ABSTRACT

The present invention relates to active substances in particulate form, to methods for preparing them and to their uses. The present invention provides particulate powders, such as might be of use for delivery using a dry powder inhaler (DPI) or similar delivery device, having properties which may be beneficial to the DPI delivery process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/622,272, filed on Sep. 18, 2012, now U.S. Pat.No. 9,339,459, which is a continuation application of U.S. patentapplication Ser. No. 10/422,342, filed on Apr. 24, 2003, now U.S. Pat.No. 8,273,330, the disclosures of which are incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to active substances in particulate form,to methods for preparing them and to their uses.

Certain pharmaceuticals may be delivered to the nose and/or lungs of apatient by inhalation, using an inhaler device of which there areseveral known types. Pulmonary delivery by aerosol inhalation hasreceived much attention as an attractive alternative to intravenous,intramuscular, and subcutaneous injection, since this approacheliminates the necessity for injection syringes and needles. Pulmonarydelivery also limits irritation to the skin and body mucosa which arecommon side effects of transdermally, iontophoretically and intranasallydelivered drugs, eliminates the need for nasal and skin penetrationenhancers (typical components of intranasal and transdermal systemsoften cause skin irritation/dermatitis), is economically attractive, isamenable to patient self-administration and is often preferred bypatients over alternative modes of administration.

Of particular interest in the context of the present invention arepulmonary delivery techniques which rely on the inhalation of apharmaceutical formulation by a patient so that the active drug withinthe dispersion can reach the distal (alveolar) regions of the lung.

A variety of aerosolization systems have been proposed to dispersepharmaceutical formulations. For example, U.S. Pat. Nos. 5,785,049 and5,740,794, the disclosures of which are herein incorporated byreference, describe exemplary active powder dispersion devices whichutilize a compressed gas to aerosolize a powder. Other types ofaerosolization systems include metered dose inhalers (MDIs), whichtypically have a drug that is stored in a propellant, and nebulizers(which aerosolize liquids using a compressed gas, usually air).

An alternative type of inhaler is known as a dry powder inhaler (DPI)and delivers the drug (or a composition containing the drug, forinstance together with a pharmaceutically acceptable excipient) in theform of a dry air-borne particulate powder. DPIs include single useinhalers such as those disclosed in U.S. Pat. Nos. 4,069,819, 4,995,385,3,991,761 and 6,230,707, and in WO-99/45986, WO-99/45987, WO-97/27892and GB-1 122 284; multi-single dose inhalers such as those disclosed inU.S. Pat. Nos. 6,032,666 and 5,873,360 and in WO-97/25086; andmulti-dose inhalers containing powder in a bulk powder reservoir such asthose disclosed in U.S. Pat. No. 4,524,769.

Particulate active substances, such as drugs, may be produced by avariety of known methods, including for example crystallisation fromsolution, anti-solvent precipitation from solution, milling,micronisation, spray drying, freeze drying or combinations of suchprocesses. Also known are particle formation processes which make use ofsupercritical or near-critical fluids, either as solvents for thesubstance of interest—as in the process known as RESS (Rapid Expansionof Supercritical Solution—see Tom & Debenedetti, J. Aerosol. Sci., 22(5), 555-584 (1991))—or as anti-solvents to cause the substance toprecipitate from another solution—as in the process known as GAS (GasAnti-Solvent) precipitation—see Gallagher et al, ACS Symp. Ser., 406, p334 (1989).

In general, however, known processes for producing inhalable drugs canoften yield particles which give less than satisfactory performance inDPI and similar delivery devices. For example, the dispersion of manyprior art dry powder formulations from inhalation devices exhibits aflow rate dependence such that dispersion of the powder from the deviceincreases with the patient's inspiratory effort. Alternatively, manyformulations require mixing or blending with larger carrier particlessuch as lactose in order to deliver the particles effectively to thedeep lung.

It would therefore be desirable to provide particulate drugs, and indeedother active substances which may need to be delivered as dry (ie,without a fluid carrier) powders using a DPI or analogous mechanism,which can demonstrate improved performance in such a context, inparticular improved dispersibility and aerosol performance in fluids andespecially in gases such as air.

SUMMARY OF THE INVENTION

The present invention provides particulate powders, such as might be ofuse for delivery using a DPI or similar delivery device, havingproperties which may be beneficial to the DPI delivery process. Theseproperties are illustrated in the examples below.

In particular, according to a first aspect, the present invention canprovide an active substance in particulate form, preferably preparedusing a SEDS™ particle formation process as defined below, whichexhibits one or more (preferably two or more, more preferably at leastthree) of the following characteristics:

a) the particles have a low surface energy. In particular, theypreferably exhibit a low value for the surface energy related parameterγ_(S) ^(D) (the dispersive component of surface free energy, as definedin the examples below, which reflects non-polar surface interactions)and/or for the parameter ΔG_(A) (the specific component of surface freeenergy of adsorption, again as defined in the examples, which reflectspolar surface interactions), for instance when compared to particles ofthe same active substance prepared using a non-SEDS™ particle formationprocess and preferably having the same or a smaller volume meandiameter. In the case of the parameter ΔG_(A), the value for the activesubstance of the present invention, for any given polar solvent, ispreferably lower by a factor of at least 1.2, preferably at least 1.4 or1.5, than that for the corresponding non-SEDS™-produced substance.

b) the particles exhibit a low surface adhesion and/or cohesiveness(which may be related to their surface energy). In particular, they mayexhibit lower adhesiveness than those of the same active substanceproduced by a non-SEDS™ particle formation process.

c) the particles show little or no tendency for aggregation (again thismay be related to their surface properties such as surface energy andadhesiveness), or at least form less stable aggregates than those of thesame active substance produced by a non-SEDS™ particle formationprocess.

d) the particles have a volume mean aerodynamic diameter of 7 μm orless, preferably 5 μm or less, more preferably 4 μm or 3 μm or less,such as from 1 to 5 μm, from 1 to 4 μm or from 1 to 2 μm.

e) the particles have a volume mean geometric diameter of 5 μm or less,preferably 4 μm or less, more preferably from 1 to 5 μm, most preferablyfrom 1 to 4 or from 2 to 4 μm.

f) the particles have a particle size distribution (x₉₀) of 10 μm orless, preferably also a value for (x₉₈) of 10 μm or less, preferablyalso a value for (x₉₉) of 10 μm or less. Typically each of these valueswill be from 0.5 to 10 μm.

g) when measured using a cascade impactor technique (at low turbulence),the particles have a particle size spread, defined as (x₉₀−x₁₀)/x₅₀, or1.3 or less, preferably of 1.25 or 1.2 or less, volume mean diameter of6 μm or less, preferably of 5.5 μm or less, more preferably of 5.2 μm orless. Their particle size spread under these conditions is preferably atleast 5%, more preferably at least 10%, still more preferably at least12%, smaller than that of the same active substance produced by anon-SEDS™ particle formation process, and their volume mean diameterpreferably at least 10%, more preferably at least 15%, still morepreferably at least 20%, smaller than that of the non-SEDS™ substance.

h) the particles are crystalline, or substantially so, and in particularare more crystalline than those of the same active substance produced bya non-SEDS™ particle formation process. Their X-ray diffraction patternsthus preferably exhibit reduced diffraction line broadening and/or ahigher signal-to-noise ratio than the X-ray diffraction patterns for thesame active substance produced by a non-SEDS™ process. The crystallineparticles may exhibit reduced crystal lattice imperfections such asstrain defects (point defects and/or dislocations) and/or size effects(grains, small-angle boundaries and/or stacking faults), as compared tocrystals of the same active substance produced by a non-SEDS™process—such imperfections tend to be associated with increased linebroadening in the X-ray diffraction patterns. In particular, theparticles may exhibit a lower crystal strain, and/or a higher crystaldomain size, than crystals of the same active substance produced by anon-SEDS™ particle formation process.

i) where the active substance is capable of existing in two or moredifferent polymorphic forms, the particles consist of only one suchform, with a purity of 99.5% w/w or greater, preferably of 99.8% w/w orgreater, with respect to the other polymorphic forms. More preferably,the active substance has a higher activation energy for conversion toone or more other polymorphic forms than does a sample of the sameactive substance prepared using a non-SEDS™ particle formation process.

j) the particles have a lower surface charge (for instance, meanspecific charge) than those of the same active substance produced by anon-SEDS™ particle formation process.

k) the particles exhibit superior powder flow properties (which may berelated to lower surface charge and/or adhesiveness) as compared tothose of the same active substance produced by a non-SEDS™ particleformation process; for instance, they may be more free-flowing and/orthey may deaggregate more efficiently when dispersed in a fluid such asin a DPI device, particularly at low turbulence and/or shear stresslevels.

l) the particles have a bulk powder density which is lower than that ofthe same active substance produced by a non-SEDS™ particle formationprocess. They preferably have a bulk powder density of less than 0.5g/cm³, more preferably of 0.4 g/cm⁻³ or less, most preferably of 0.2g/cm⁻³ or less.

m) the particles have a specific surface area which is higher than thatof the same active substance produced by a non-SEDS™ particle formationprocess.

n) the “shape factor” of the particles, by which is meant the ratio of(a) their measured specific surface area (ie, surface area per unitvolume) to (b) their theoretical specific surface area as calculatedfrom their measured diameters assuming spherical particles, is higherthan that of the same active substance produced by a non-SEDS™ particleformation process. Preferably this shape factor is at least 2, morepreferably at least 3, most preferably at least 3.5.

o) the “shape coefficient”, α_(S,V) of the particles, determined fromimage (eg, SEM) analysis and as defined in the following equation:α_(S,V)≅6d _(s) ³ /d _(v) ³

where the mean projected diameter, d_(s), is given by:d _(s)=(4S/π)^(1/2)=((2/π)(ab+bc+ca))^(1/2) and

the volume particle diameter, d_(v), is given byd _(v)=(6V/π)^(1/3)=(6abc/π)^(1/3)

is higher than that of the same active substance produced by a non-SEDS™particle formation process, preferably at least 1.5 times as great, morepreferably at least twice as great. Preferably this shape coefficient isat least 10, more preferably at least 15, most preferably at least 18 orat least 20. It may alternatively be calculated from specific surfacearea measurements, laser diffraction particle size measurements and thetheoretical crystal density, as defined in the following equation:S _(v)=α_(S,V)/ρ_(xmin)∫^(xmax) x ⁻¹ q ₃(x)dx

p) the “aerodynamic shape factor” of the particles, χ, is greater thanthat for the same active substance produced by a non-SEDS™ particleformation process, preferably at least 20% greater, more preferably atleast 30% or at least 40% greater χ is the ratio of the drag force on aparticle to the drag force on the particle volume-equivalent sphere atthe same velocity, and may be calculated as described in the followingequation:χ≅((C _(d)(d _(S))C _(c)(d _(V)))/(C _(d)(d _(V))C _(c)(d _(S))))(d _(S)/d _(V))²

For a product according to the invention it may be 1.4 or greater,preferably 1.5 or greater, most preferably 1.7 or 1.8 or greater.

q) the particles have reduced surface roughness compared to those of thesame active substance produced by a non-SEDS™ particle formationprocess.

By “non-SEDS™ particle formation process” is meant a particle formationprocess other than the non-SEDS™ process defined below, for example oneinvolving micronisation, granulation and/or solvent crystallisationunder sub-critical conditions, and in particular one involvingmicronisation. In general, comparisons between substances according tothe invention and those made by non-SEDS™ techniques are suitably madeusing in each case particles of the same or a comparable size (eg, nomore than 30% or even than 20% different in size) and/or shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the percentage dissolution against time for particlesprocessed according to the invention compared to micronised.

FIG. 2 depicts an AFM analysis of material process according to thisinvention.

FIG. 3 is a graph showing RMS surface roughness data for materialsprocessed according to the invention.

FIG. 4 is a schematic of the SEDS process.

FIGS. 5A-5C depict X-ray powder patterns illustrating the crystallinityof micronised and samples produced according to the invention.

FIG. 6 depicts the heat flow (μW) for both micronised and SEDS™ powdersof terbutaline sulphate.

FIGS. 7A and 7B depict the strange attractor plots for terbutalinesulphate analysed at high (100 seconds per revolution) rotation speed.

FIGS. 8A and 8B depict the strange attractor plots for TBS analysed atmedium (145 seconds per revolution) rotation speed.

FIGS. 9 and 10 compare the in vitro performance of micronised and SEDS™processed terbutaline sulphate analysed in a lactose blend as well aspure drug alone.

DETAILED DESCRIPTION

It has been found that particulate active substances having one or moreof the above properties tend to exhibit improved performance, inparticular good dispersibility, in delivery devices such as inhalers,especially dry powder inhalers and more especially passive dry powderinhalers. In particular a correlation has been found between lowerparticle surface energy and improved DPI performance. Similarly, lowerstrain, higher crystallinity and higher polymorphic purity have beenassociated with reduced agglomeration and particle adhesion, and withlower electrostatic charge, again properties which lead to improved DPIperformance. Higher specific surface areas, and higher shape factors,have also been found to accompany improved DPI performance. For a givenparticle size, products according to the invention can demonstratesignificantly better performance in passive dry powder inhalers thanproducts made by conventional techniques such as spray drying, freezedrying, granulation and in particular micronisation.

Thus, the active substance of the invention, when used in a passive drypowder inhaler or analogous delivery device (for example thecommercially available Clickhaler™), preferably yields a fine particlefraction in the emitted dose of 20% or greater, preferably 26% orgreater, more preferably 31% or greater, in cases 35% or 40% or 50% oreven 55% or greater. Instead or in addition, its fine particle fractionmay be at least 20% greater, preferably at least 25% or 30% or 40% or50% or 60% or 80% or 100% greater, more preferably at least 110% or 120%or 130% or 140% greater, than that of the same active substance producedby a non-SEDS™ particle formation process and having the same or asmaller volume mean diameter.

The active substance is preferably in a substantially (eg, 95% w/w;preferably 98% or 99% w/w or greater) pure form. It preferably containslow levels of residual solvent, for example less than 500 ppm, morepreferably less than 200 ppm, most preferably less than 150 or 100 ppmresidual solvent, by which is meant solvent(s) which were present at thepoint of particle formation. Still more preferably the substancecontains no detectable residual solvent, or at least only levels belowthe relevant quantification limit(s). In particular residual solventlevels in the bulk particles, as opposed to merely at their surfaces,are likely to be lower than in particles of the same active substanceproduced by a non-SEDS™ process.

In cases, the fine particle fraction yielded by an active substanceaccording to the invention, for instance in an Andersen™ cascadeimpactor, may be up to 150% or 175% or even 200% or 250% or 280% of thatof the same active substance produced by a non-SEDS™ process. Suchimprovements may often be exhibited even if the particle size of thesubstance of the invention is significantly greater (eg, at least 30% or50% or 75% or 90% greater) than that of the non-SEDS™-producedsubstance. They can also be exhibited in the absence of dispersionenhancing additives such as surfactants, in the absence ofexcipient/carrier materials and/or in unimodal (with respect to particlesize) systems.

Particular improvements (with respect to substances made by non-SEDS™processes) may be seen where the active substance is used alone asopposed to in a blend with an excipient such as lactose.

The total emitted dose for a substance according to the invention mayalso, in this context, be at least 10% greater, preferably at least 15%greater, more preferably at least 20% or 25% or 30% greater, than thatfor the same active substance made by a non-SEDS™ process, either withor without excipient(s). Generally the substances of the invention maydeposit on the impactor stages with a narrower distribution (typicallyweighted more to the lower stages such as 1 to 3) than for those made bynon-SEDS™ processes.

At relatively low dispersing pressures, for instance 2 bar or less, anactive substance according to the invention has been found capable ofyielding a significantly higher proportion of primary particles in therespirable size range than the same active substance produced by anon-SEDS™ process, the latter often tending to form stable (ie, notdispersible at these pressures) agglomerates above the preferred 5 μmlimit. This again indicates reduced particle cohesiveness and/or reducedinter-particulate contact area in an active substance according to theinvention. The volume mean particle diameter d_(4,3) of the particles ofthe invention (calculated from cascade impactor data) may thus appearlarger than that for non-SEDS™-produced particles when dispersed atpressures of 2 bar and above, but smaller at pressures below 2 bar, forinstance 1.8 bar or below, where the dispersion (or deaggregation)ability of the particles plays a more dominant role.

Since the viscous shear stress within the impactor will affect thedispersion behaviour of the particles and hence their apparent volumemean diameter, particles according to the invention exhibit volume meandiameters lower than those of their non-SEDS™ equivalents at lowerviscous shear stresses, for instance below 20 Nm⁻² or even up to 30 or40 Nm⁻².

At such low shear stress levels, particles according to the inventionappear to undergo significantly less aggregation, or to formsignificantly less stable aggregates, than those produced by a non-SEDS™process which may produce stable aggregates well outside the 5 μmrespirable limit. The particles of the invention, at these shear stresslevels (or at least at shear stress levels between 5 and 30 Nm⁻² orbetween 10 and 30 Nm⁻²) can produce a large fraction of primaryparticles in the respiratory size range, preferably having a volume meandiameter of less than 6 or more preferably less than 5 μm.

Thus, the volume mean particle diameter of an active substance accordingto the invention, derived from cascade impactor data in the mannerdefined in the Examples below, may be at least 10% smaller, preferablyat least 15% or at least 20% smaller, than that of the same activesubstance produced by a non-SEDS™ particle formation technique, evenwhere its volume mean diameter measured at higher dispersions usinganother technique such as laser diffraction or time-of-flight is greaterthan (for instance, up to 30% or 50% or even 100% greater than) that ofthe non-SEDS™ substance. This indicates that for a given size, particlesaccording to the invention can give superior performance onaerosolisation.

Accordingly, particulate active substances of the present invention maybe particularly advantageous for use with passive dry powder inhalerswhich operate in the lower region of turbulent stresses when dispersingthe powder they contain.

In the context of the present invention, a passive dry powder inhaler isa device for use in delivering a powdered active substance to a patient,in which the patient's inspiratory effort is used as the sole powderdispersing means. In other words, the powder is not delivered in apressurised fluid as in many metered dose inhalers, and nor does itsdelivery require the use of a rotating impeller or other mechanicalmeans.

A second aspect of the present invention provides a method for selectinga particulate active substance for use in a dry powder inhaler, inparticular a passive dry powder inhaler, which method involves theassessment of, and selection on the basis of, one or more (preferablytwo or more, more preferably three or more) of the above describedproperties of active substances according to the first aspect of theinvention.

A third aspect provides the use of an active substance according to thefirst aspect, in a dry powder inhaler and in particular in a passive drypowder inhaler, for the purpose of achieving improved active substancedelivery. Improved delivery in this context may involve improved powderdispersion, more accurate dosage delivery, more consistent dosagedelivery and/or a higher fine particle fraction in the emitted dose, inparticular at relatively low dispersing pressures such as 2 bar or lessor 1.8 bar or less.

Particle surface energies may be measured using inverse gaschromatography (IGC), for instance using a gas chromatograph from theHewlett Packard™ series. Surface energy measurements ideally takeaccount of the dispersive component of the surface free energy, γ_(S)^(D), the specific component of the surface free energy of adsorption,ΔG_(A), the acid-base parameters and/or the total (Hildebrand)solubility parameter, which takes into account dispersive, polar andhydrogen-bonding interactions on particle surfaces and thus reflects theinter-particle adhesion. The dispersive component may be assessed usingnon-polar probes such as alkanes, and the specific component ΔG_(A) maybe assessed using data from both polar and non-polar probes, the formerhaving both dispersive and specific components of surface free energy ofadsorption.

Thus, gas chromatography measurements suitably involve the use of bothnon-polar and polar probes, examples of the former being alkanes such aspentane, hexane, heptane, octane and nonane and of the latter beingdiethyl ether, toluene, acetone, ethyl acetate, chloroform, dioxane,dichloromethane and tetrahydrofuran.

In the case of the dispersive component γ_(S) ^(D), the value for theactive substance of the present invention is preferably at least 5%lower, more preferably at least 10% lower, most preferably at least 12%or 15% or 20% or 30% lower, than that for the same active substance madeby a non-SEDS™ particle formation process.

In the case of the specific component ΔG_(A), the value for the activesubstance of the present invention is preferably at least 10% lower,more preferably at least 15% lower, most preferably at least 20% or 30%or 50% or 80% lower, than that for the same active substance made by anon-SEDS™ particle formation process.

In the case of the Hildebrand solubility parameter δ, the value for theactive substance of the present invention is preferably at least 5%lower, more preferably at least 8% lower, most preferably at least 10%lower, than that for the same active substance made by a non-SEDS™particle formation process.

Overall, particulate active substances according to the presentinvention tend to have lower surface activity (for example with respectto solvent adsorption) and greater surface stability than those producedby non-SEDS™ particle formation processes, with a more ordered surfacestructure. Their lower surface energy may be manifested by a lower valuefor K_(A) and/or K_(D), for instance as measured in Example 2,indicative of weaker acidic and/or basic interactions respectively atthe particle surfaces. For instance, their K_(A) may be at least 5%,preferably at least 10% or at least 12%, lower than that of the sameactive substance made by a non-SEDS™ particle formation process, and/ortheir K_(D) may be at least 30%, preferably at least 50% or at least 60%lower.

The specific surface energy E_(S) of a particulate active substanceaccording to the invention, calculated as per the following equation:E _(s)=0.683(δ²/α_(S,V) ^(2/3))Ω^(1/3)

where δ is the Hildebrand solubility parameter, α_(S,V) is the shapecoefficient, and Ω is the molecular volume is preferably at least 10%,more preferably at least 20%, still more preferably at least 30% or 40%,lower than that of the same active substance produced by a non-SEDS™particle formation process, and might typically be 100 mJ/m² or lower,more preferably 90 or 80 or 70 mJ/m² or lower.

A lower aggregation tendency in particles according to the invention maybe reflected in a lower theoretical aggregate tensile strength σ, whichmay be calculated as described in the following equation:σ≅15.6(ρ_(B)/ρ_(C))⁴ W/d _(s)

where ρ_(B) and ρ_(C) are the bulk density and particle crystal density,respectively, and W is the work of adhesion. Preferably the ratio of σfor particles of the invention to that for particles of the same activesubstance produced by a non-SEDS™ process is 0.8 or lower, morepreferably 0.5 or lower, most preferably 0.3 or 0.2 or 0.1 or lower,especially when polar interactions are taken into account.

Similarly, the aerodynamic stress required to disperse aggregates ofparticles according to the invention (for instance, calculated fromcascade impactor measurements, as described in the Examples below) istypically lower than that required to disperse aggregates of the sameactive substance prepared by a non-SEDS™ particle formation process.Ideally the ratio of the two stresses (SEDS™ product:non-SEDS™ product)is 0.8 or lower, more preferably 0.5 or lower, most preferably 0.3 or0.2 or lower. Inter-particle aggregation can be particularly relevant toDPI performance since such aggregates tend to survive the pre-separationstage. Aggregation tendencies can also be relevant when an activesubstance is blended with a carrier such as lactose, where dispersionmay depend on the break-up of active-carrier aggregates—again,typically, substances according to the invention may tend to form lessstable aggregates with carrier particles.

Particle sizes may be measured for instance using (a) an AeroSizer™time-of-flight instrument (which gives a mass mean aerodynamicequivalent particle diameter, MMAD, measured at Reynolds numbers greaterthan 1) or (b) a laser diffraction sensor such as the Helos™ system(which provides a geometric projection equivalent mass median diameter).Volume mean aerodynamic and geometric diameters respectively may beobtained from these measurements using commercially available softwarepackages.

The aerodynamic diameter d_(A) of a particulate active substanceaccording to the invention, measured according to the examples below, ispreferably 2 μm or below, more preferably 1.8 μm or below, mostpreferably 1.6 μm or below.

Particle size distributions may be measured using laser diffractionand/or time-of-flight measurements, for instance using an AeroSizer™time-of-flight instrument equipped with an AeroDisperser™ (TSI Inc,Minneapolis, USA) and/or a Helos™ laser diffraction sensor with Rodos™dry powder air dispersion system (Sympatec GmbH, Germany). Volumeparticle size distributions based on aerodynamic equivalent particlediameters are preferred. Ideally time-of-flight measurements aregathered at high shear forces, high deaggregation levels and/or low feedrates, in order to facilitate production of primary aerosol particles.

Particle size distribution (PSD) data, in particular obtained by laserdiffraction measurements, may also be used to calculate the shapecoefficient α_(S,V) of particles in the manner described above.

An active substance according to the invention will suitably have acumulative particle size distribution such that more than 98% of theparticles are within the respirable particle size range from 0.5 to 10μm.

Scanning electron microscopy (SEM) may also be used to measurecharacteristic particle dimensions and thus characteristics such asparticle aspect ratios and shape factors.

Crystallinity of a particulate material may be determined using X-raypowder diffraction, preferably high resolution X-ray powder diffractionsuch as using a synchrotron radiation source. Using commerciallyavailable software, X-ray diffraction data may be employed to assess thedistribution of crystalline domain sizes and the degree of strain in thecrystals.

X-ray diffraction line broadening can provide an indication of crystallattice imperfections such as strain defects (point defects ordislocations) and size effects (grains, small-angle boundaries orstacking faults). Line broadening may be manifested for instance by anincreased peak width (eg, full width at half maximum height, FWHM)and/or an increased integral breadth β* (the width of rectangle havingthe same area A and height I as the observed line profile, ie, β*=A/I),for one or more of the diffraction peaks.

Preferably, for at least one peak in its X-ray diffraction pattern(ideally for two or more, even three or more, peaks), the activesubstance of the invention exhibits a FWHM which is at least 20% lower,more preferably at least 25% lower, most preferably at least 30% or 40%or 50% lower, than that of the corresponding peak (ie, the peak for thesame crystal plane) in the X-ray diffraction pattern of the samesubstance produced by a non-SEDS™ particle formation process. The FWHMof at least one, ideally of at least two or three or even of all, peaksis preferably 0.1° or less, more preferably 009°. or less, mostpreferably 0.08° or less.

For at least one peak in its X-ray diffraction pattern (ideally for twoor more, even three or more, peaks), the active substance of theinvention preferably exhibits an integral breadth β* which is at least20% lower, more preferably at least 25% lower, most preferably at least30% or 40% or 45% lower, than that of the corresponding peak in theX-ray diffraction pattern of the same substance produced by a non-SEDS™particle formation process. The integral breadth of at least one,ideally of at least two or three or even of all, peaks is preferably0.11° or less, more preferably 0.1° or less.

A reduced level of crystal lattice imperfections, in a particulateproduct according to the invention, may also be manifested by a shift inposition, towards higher 2θ values (typically a shift of 0.0005°. ormore, such as of from 0.0005 to 0.005 or from 0.001 to 0.0030°, of oneor more of the diffraction peaks. This may be associated with a decreasein crystal d-spacing (Δd/d) of 0.5% or more, typically 1% or more, suchas from 1 to 2%, in the product of the invention, and with acorresponding reduction in crystal volume, ΔV/V, of 0.5% or more,typically 1% or more, such as from 1 to 2%.

Levels of crystal lattice imperfections may also be assessed withreference to the crystal domain sizes and/or the crystal strain. Domainsizes are typically significantly greater for products according to theinvention, compared to the same active substance produced using anon-SEDS™πparticle formation process, and crystal strain is typicallysignificantly lower. Such parameters may be calculated from X-raydiffraction patterns, for instance by analysing the diffraction peakprofiles as a convolution of Cauchy and Gauss integral breadthscontaining size and strain (distortion) contributions, as known in theart. This allows calculation of for example surface-weighted (D_(V))and/or volume weighted (D_(S)) domain sizes, and of a mean-square(Gaussian) strain, ε, which is the total strain averaged over infinitedistance.

Preferably, the active substance of the invention exhibits asurface-weighted domain size D_(S) which is at least 15% higher, morepreferably at least 20% higher, most preferably at least 30% or 35%higher, than that of the same substance produced by a non-SEDS™ particleformation process. It preferably exhibits a volume-weighted domain sizeD_(V) which is at least 10% higher, more preferably at least 15% higher,most preferably at least 20% or 25% higher, than that of the samesubstance produced by a non-SEDS™ particle formation process. D_(S) mayfor example be 400 Å or greater, and D_(V) may be 700 Å or greater, inan active substance according to the invention.

Preferably the active substance of the invention exhibits a total strainε which is at least 30% lower, more preferably at least 35% lower, mostpreferably at least 40% or 45% lower, than that of the same substanceproduced by a non-SEDS™ particle formation process. Its total strain mayfor instance be 0.7×10⁻³ or lower, preferably 0.6×10⁻³ or lower, mostpreferably 0.5×10⁻³ or lower.

Domain size and strain may alternatively be calculated from the X-raydiffraction data by Le Bail diffraction profile fitting. Using suchcomputational methods, an active substance according to the inventionpreferably exhibits a volume-weighted domain size which is at least 50%higher, more preferably at least 80% higher, most preferably at least90% higher, than that of the same substance produced by a non-SEDS™particle formation process. It preferably exhibits a strain which is atleast 40% lower, more preferably at least 50% lower, most preferably atleast 60% lower, than that of the same substance produced by a non-SEDS™particle formation process.

An active substance according to the invention may have an amorphouscontent of less than 5% w/w, preferably less than 2% w/w, morepreferably less than 1 or even than 0.5 or 0.2% w/w. Ideally itsamorphous phase content is at least 10 times, preferably at least 20 oreven 40 or 50 times, lower than that of the same active substanceproduced by a non-SEDS™ particle formation process.

A higher bulk crystallinity, in an active substance according to theinvention, may be manifested by a lower moisture uptake at any giventemperature and humidity, and/or by a thermal activity profile with noexothermic or endothermic peaks, for instance as measured in theexamples below.

Polymorphic purity may be assessed for instance using melting point data(eg, differential scanning calorimetry) or more preferably using X-raypowder diffraction (for instance the small-angle X-ray scattering (SAXS)technique) to detect polymorphic transitions during heating, based onthe diffraction peaks characteristic of the polymorphs.

An active substance according to the invention is preferably morestable, with respect to polymorphic transitions, than a sample of thesame active substance prepared using a non-SEDS™ particle formationprocess; it will thus typically have a higher activation energy forconversion to one or more other polymorphic forms than will thenon-SEDS™ sample for the same polymorphic transition. More preferably,when heated at a rate of 10° C. per minute or greater at atmosphericpressure, the active substance of the invention will not alter itspolymorphic form. Instead or in addition, the time required forformation of one or more other polymorphs of the active substance,calculated for instance from X-ray diffraction and thermal analysisdata, is preferably 80 seconds or greater, more preferably 90 seconds orgreater. The active substance preferably contains no detectable seednuclei of polymorphic forms other than that desired to be present.

Enhanced crystallinity and/or polymorphic purity in active substancesaccording to the invention are believed to contribute to an overallhigher physical stability as compared to the same active substancesprepared using non-SEDS™ particle formation techniques.

Surface electric charge may be assessed as specific charge. Theelectrostatic charge carried by a particulate material may be measuredfor instance in a Faraday well. Alternatively the particulate materialmay for instance be subjected to triboelectrification by agitating itagainst an electrically conductive contact surface, for example in aturbula mixer or cyclone separator, and its charge and mass determinedboth before and after triboelectrification, suitably using anelectrometer, to give a value for specific charge. This process may alsobe used to give a measure of the adhesion properties of the particles,by measuring the mass of the original sample and that removable from themixer/separator in which it was agitated and calculating the weightpercentage of the sample lost by adhesion to the contact surface(s) ofthe vessel.

Adhesion may also be assessed using a simple test of the type describedin Examples 3 below, in which a sample is agitated in a container, andthe non-adhering material then removed from the container and weighed,to allow calculation of the percentage of the original sample adheringto the container surfaces.

By way of example, an active substance according to the inventionpreferably has a mean specific charge of from −5 to +5 nCg⁻¹, morepreferably from −1 to +1 nCg⁻¹, and/or a mean specific charge which isat least 50%, preferably at least 70%, most preferably at least 80% or90% or 95%, lower than that of the same active substance produced by anon-SEDS™ particle formation process.

Following triboelectrification using a Turbula™ mixer, an activesubstance according to the invention preferably has a mean specificcharge which is at least 30% lower, more preferably at least 50% lower,most preferably at least 75% or 80% or 90% or 95% lower, than that ofthe same active substance produced by a non-SEDS™ process. Followingtriboelectrification using a cyclone separator, an active substanceaccording to the invention preferably has a mean specific charge whichis at least 30% lower, more preferably at least 50% lower, mostpreferably at least 75% or 80% or 85% lower, than that of the sameactive substance produced by a non-SEDS™ process.

The mean adhesion fraction (ie, the fraction of adhered material)assessed in the manner described above following triboelectrification ina turbula mixer, is preferably 20% w/w or less, more preferably 10% w/wor less, most preferably 5% or 2% w/w or less, for an active substanceaccording to the invention. It is preferably at least 50% lower, morepreferably at least 75% lower, most preferably at least 80% or 90%lower, for an active substance according to the invention than for thesame active substance produced by a non-SEDS™ process.

The mean adhesion fraction, assessed in the manner described abovefollowing triboelectrification in a cyclone separator, is preferably 20%w/w or less, more preferably 10% w/w or less, most preferably 5% w/w orless, for an active substance according to the invention. It ispreferably at least 40% lower, more preferably at least 50% lower, mostpreferably at least 60% or 65% lower, for an active substance accordingto the invention than for the same active substance produced by anon-SEDS™ process.

In cases, an active substance produced by a non-SEDS™ process mayexhibit at least 5 times as much adhesion as the same active substanceproduced by a SEDS™ process, preferably at least 8 times or at least 10times or at least 15 times that of the SEDS™ substance.

The adhesion force per unit area to a highly oriented pyrolytic graphitesubstrate assessed using atomic force microscopy in the manner describedabove is preferably less than 60% of, more preferably less than 30% of,most preferably less than 15% of that for particles of the same activesubstance produced by a non-SEDS™ process.

Powder flow properties may be assessed by analysing the dynamicavalanching behaviour of a particulate product, such as using anAeroflow™ powder avalanching apparatus (Amherst Process Instruments,Amherst, USA), for instance as described in the Examples below.

Superior powder flow properties, in an active substance according to theinvention, may be manifested by a strange attractor plot which is closerto the origin and/or has a smaller spread than that for the same activesubstance produced by a non-SEDS™ process. A strange attractor plot maybe obtained, again as described in the examples below, from powderavalanching data (in particular, time intervals between avalanches)using the method of Kaye et al, Part. Charact., 12 (1995), 197-201.Substances according to the invention tend to exhibit lower meanavalanche times (for example at least 5% or even 8% lower at 100 s/rev,at least 10% or even 14% lower at 145 s/rev) than corresponding productsof non-SEDS™ processes. They may show a lower irregularity of flow (forexample at least 5% or even 8% lower at 100 s/rev, at least 8% or even10% lower at 145 s/rev) than corresponding non-SEDS™ products,irregularity of flow being assessed in terms of avalanche scatter.

The bulk powder density of an active substance according to theinvention may be measured in conventional manner, for example using avolumetric cylinder, and is preferably at least 20% lower, morepreferably at least 50% lower, most preferably at least 60% or 70% or80% lower, than that of the same active substance produced by anon-SEDS™ process. Its aerosolised powder bulk density is preferably atleast 10%, more preferably at least 20%, lower. It has been found thatactive substances according to the invention may, surprisingly, haveboth relatively low bulk powder densities yet also good powder flowproperties in particular lower cohesiveness and adhesiveness and/or alower tendency to accumulate static charge.

Specific surface area of particles may be determined by conventionalsurface area measuring techniques such as low temperature physicaladsorption of nitrogen (eg, BET nitrogen adsorption using a Surface AreaAnalyser Coulter™ SA 3100 (Coulter Corp., Miami, USA)). Preferably thespecific surface area of a particulate active substance according to theinvention is at least 1.2 or 1.5 times, more preferably at least twice,still more preferably at least 3 times, most preferably at least 4 or4.5 times, that of the same active substance produced by a non-SEDS™process. Typically an active substance according to the invention mighthave a specific surface area of at least 10 m²/g, preferably at least 15or 20 or 25 m²/g, and/or a surface-to-volume ratio of at least twice,preferably at least 2.5 times, that of spherical particles of the samevolume diameter.

The shape factor f may suitably be calculated as f=Sv/Sv*, where Sv isthe experimentally determined (eg, by BET nitrogen adsorption) specificsurface area and Sv* the specific surface area calculated from particlesize measurements (eg, those obtained by laser diffraction) assumingspherical particles. An active substance preferably has a shape factor fwhich is at least 20%, more preferably at least 30%, larger than that ofthe same active substance (suitably having the same or a comparablecrystal shape and particle size) produced by a non-SEDS™ particleformation process. Thus, particles of an active substance according tothe invention preferably have a higher available surface area thanparticles of the same active substance made by a non-SEDS™ process—wherefor instance the particles are in the form of platelets or needles,those of the present invention may thus be thinner than those producedby non-SEDS™ techniques.

A typical shape factor f for a particulate active substance according tothe invention might for instance be 3 or greater, preferably 3.2 orgreater, more preferably 3.5 or greater, most preferably 3.7 or greater.

A higher specific surface area and/or shape factor appears, in an activesubstance according to the invention, to accompany improved dissolutionperformance as compared to the same active substance produced by anon-SEDS™ particle formation process. In particular, a product accordingto the invention may dissolve more rapidly in any given solvent and withgreater efficiency, for instance with at least 40% higher dissolution,more preferably at least 50% higher dissolution than the non-SEDS™product after a period of 150 or even 300 minutes, ideally the SEDS™product achieving complete dissolution after a period of 50 minutes orless. Such improved dissolution is particularly advantageous for poorlysoluble (generally poorly aqueous soluble) materials.

Surface roughness may be assessed using AFM analysis; reduced roughnessmay be indicated for instance by a reduced RMS roughness. Particles ofan active substance according to the invention preferably have a RMSroughness, measured using AFM, of 0.5 nm or less, preferably 0.3 or 0.2nm or less. Their RMS roughness is preferably at least 70% lower, morepreferably at least 80% or 90% lower, than that of the same activesubstance prepared by a non-SEDS™ particle formation process.

Deposition properties of an active substance, in particular fineparticle fractions, may be measured using the cascade impactortechnique, for instance using an Andersen™-type cascade impactor (CopleyScientific Ltd, Nottingham, UK). Such devices imitate particledeposition in the lungs from a dry powder inhaler. High fine particlefractions are preferred, with respect to delivery to stages 1 to 5 ofthe impactor. Thus, fine particle fractions are preferably measured asthe mass of particles having an efficient cut-off diameter (ECD) ofbetween 0.5 and 5 μm, for instance as described in the examples below.From the cascade impactor data, an apparent volume mean diameter mayalso be calculated as known in the art.

HPLC may be used for quantitative analysis of the active substancecontent in the material deposited at each stage of the impactor and ifapplicable in associated apparatus such as pre-separator, throat ormouthpiece.

For the purpose of assessing fine particle fraction, the activesubstance of the invention may be blended with a suitable excipient,preferably a pharmaceutically acceptable excipient suitable for deliveryto the lung, a common example being lactose. Such a blend mighttypically contain from 1 to 10% w/w of the active substance, preferablyfrom 2 to 5% w/w. Again because of the advantageous properties of theactive substance of the invention, for instance its lower surface energyand adhesiveness, it tends to be better able to detach from theexcipient, under these conditions, than the same active substanceprepared by a non-SEDS™ process; in other words, it forms less strongaggregates with the excipient.

The active substance of the invention is preferably in the form of solid(eg, as opposed to hollow, porous or at least partiallyfluid-containing) particles. It is preferably in a crystalline orsemi-crystalline (as opposed to amorphous) form, more preferablycrystalline.

In particular it preferably has a crystalline form which issignificantly longer in one dimension than in at least one otherdimension (ie, it has a relatively high aspect ratio); this embraces forexample needle-like crystals and also, potentially, wafer-, blade- orplate-like crystals (which are longer in two dimensions than in thethird) and elongate prism-shaped crystals. These have been found to showbetter DPI performance than correspondingly sized particles of othershapes. Needle-like (acicular) or platelet-shaped crystals may beparticularly preferred.

In the above discussion, “significantly” longer means at least 5%,preferably at least 10% or 20% or 30%, greater than the length of thelower of the two parameters being compared.

As discussed above, particles according to the invention if in the formof platelets or needles are typically thinner than those of the sameactive substance produced by a non-SEDS™ process (as reflected by forinstance a difference in shape factors, shape coefficients and specificsurface areas). When examined for example by SEM, the particles of theinvention can often be seen to have less rounded edges and cornersand/or to be less fragmented than those of the non-SEDS™ substance inparticular a micronised substance—this may be reflected in a lowersurface energy, lower particle adhesion and/or lower tendency foraggregation in the product of the invention.

In general, the behaviour of an active substance according to thepresent invention on aerosolisation, which in turn affects itssuitability for respiratory drug delivery and in particular for DPIdelivery, may be assessed and characterised using the techniquesoutlined in the examples below. These can involve assessing the size,surface characteristics, aerodynamic properties, deagglomerationbehaviour and/or solid state properties of the active substanceparticles. Such techniques may be used for instance in the selectionmethod of the second aspect of the invention.

By “active substance” is meant a substance capable of performing someuseful function in an end product, whether pharmaceutical, pesticidal orwhatever. The term is intended to embrace substances whose function maybe as an excipient for another substance.

The active substance may be a single active substance or a mixture oftwo or more. It may be monomeric, oligomeric or polymeric, organic(including organometallic) or inorganic, hydrophilic or hydrophobic. Itmay be a small molecule, for instance a synthetic drug like paracetamol,or a macromolecule such as a protein or peptide (including enzymes,hormones, antibodies and antigens), nucleotide, nucleoside or nucleicacid. Other potential active substances include vitamins, amino acids,lipids including phospholipids and aminolipids, carbohydrates such aspolysaccharides, cells and viruses.

The active substance preferably comprises (more preferably is) apharmaceutically or nutriceutically active substance, or apharmaceutically or nutriceutically acceptable excipient, or a mixtureof two or more thereof. More preferably it is a pharmaceutically activesubstance or mixture thereof which is suitable for delivery byinhalation (which term includes nasal and/or oral inhalation), althoughin general it may be any active substance which is deliverable as a drypowder, ideally using a passive dry powder inhaler. Many other activesubstances, whatever their intended function (for instance, herbicides,pesticides, foodstuffs, imaging agents, dyes, perfumes, cosmetics andtoiletries, detergents, coatings, products for use in the ceramics,photographic or explosives industries, etc.) are embraced by the presentinvention.

Of particular interest for delivery by inhalation are pharmaceuticallyactive substances which need to be delivered systemically and requirerapid onset of action. According to a preferred embodiment, formulationsare provided which achieve a maximum concentration of a pharmaceuticallyactive substance, C_(max) within 1 hour of administration, preferablywithin 30 minutes, and most preferably within 15 minutes. This time toachieve maximum concentration of the active substance is referred toherein as T_(max).

Examples of pharmaceutically active substances which may be delivered byinhalation include β₂-agonists, steroids such as glucocorticosteroids(preferably anti-inflammatories), anti-cholinergics, leukotrieneantagonists, leukotriene synthesis inhibitors, pain relief drugsgenerally such as analgesics and anti-inflammatories (including bothsteroidal and non-steroidal anti-inflammatories), cardiovascular agentssuch as cardiac glycosides, respiratory drugs, anti-asthma agents,bronchodilators, anti-cancer agents, alkaloids (eg, ergot alkaloids) ortriptans such as can be used in the treatment of migraine, drugs (forinstance sulphonyl ureas) useful in the treatment of diabetes andrelated disorders, sleep inducing drugs including sedatives andhypnotics, psychic energizers, appetite suppressants, anti-arthritics,anti-malarials, anti-epileptics, anti-thrombotics, anti-hypertensives,anti-arrhythmics, anti-oxicants, anti-depressants, anti-psychotics,auxiolytics, anti-convulsants, anti-emetics, anti-infectives,anti-histamines, anti-fungal and anti-viral agents, drugs for thetreatment of neurological disorders such as Parkinson's disease(dopamine antagonists), drugs for the treatment of alcoholism and otherforms of addiction, drugs such as vasodilators for use in the treatmentof erectile dysfunction, muscle relaxants, muscle contractants, opioids,stimulants, tranquilizers, antibiotics such as macrolides,aminoglycosides, fluoroquinolones and beta-lactams, vaccines, cytokines,growth factors, hormonal agents including contraceptives,sympathomimetics, diuretics, lipid regulating agents, antiandrogenicagents, antiparasitics, anticoagulants, neoplastics, antineoplastics,hypoglycemics, nutritional agents and supplements, growth supplements,antienteritis agents, vaccines, antibodies, diagnostic agents, andcontrasting agents and mixtures of the above (for example the asthmacombination treatment containing both steroid and β-agonist). Moreparticularly, the active agent may fall into one of a number ofstructural classes, including but not limited to small molecules(preferably insoluble small molecules), peptides, polypeptides,proteins, polysaccharides, steroids, nucleotides, oligonucleotides,polynucleotides, fats, electrolytes, and the like.

Specific examples include the β₂-agonists salbutamol (eg, salbutamolsulphate) and salmeterol (eg, salmeterol xinafoate), the steroidsbudesonide and fluticasone (eg, fluticasone propionate), the cardiacglycoside digoxin, the alkaloid anti-migraine drug dihydroergotaminemesylate and other alkaloid ergotamines, the alkaloid bromocriptine usedin the treatment of Parkinson's disease, sumatriptan, rizatriptan,naratriptan, frovatriptan, almotriptan, zolmatriptan, morphine and themorphine analogue fentanyl (eg, fentanyl citrate), glibenclamide (asulphonyl urea), benzodiazepines such as vallium, triazolam, alprazolam,midazolam and clonazepam (typically used as hypnotics, for example totreat insomnia or panic attacks), the anti-psychotic agent risperidone,apomorphine for use in the treatment of erectile dysfunction, theanti-infective amphotericin B, the antibiotics tobramycin, ciprofloxacinand moxifloxacin, nicotine, testosterone, the anti-cholenergicbronchodilator ipratropium bromide, the bronchodilator formoterol,monoclonal antibodies and the proteins LHRH, insulin, human growthhormone, calcitonin, interferon (eg, β- or γ-interferon), EPO and FactorVIII, as well as in each case pharmaceutically acceptable salts, esters,analogues and derivatives (for instance prodrug forms) thereof.

Additional examples of active agents suitable for practice with thepresent invention include but are not limited to aspariginase, amdoxovir(DAPD), antide, becaplermin, calcitonins, cyanovirin, denileukindiftitox, erythropoietin (EPO), EPO agonists (e.g., peptides from about10-40 amino acids in length and comprising a particular core sequence asdescribed in WO 96/40749), domase alpha, erythropoiesis stimulatingprotein (NESP), coagulation factors such as Factor VIIa, Factor VIII,Factor IX, von Willebrand factor; ceredase, cerezyme, alpha-glucosidase,collagen, cyclosporin, alpha defensins, beta defensins, exedin-4,granulocyte colony stimulating factor (GCSF), thrombopoietin (TPO),alpha-1 proteinase inhibitor, elcatonin, granulocyte macrophage colonystimulating factor (GMCSF), fibrinogen, filgrastim, growth hormones,growth hormone releasing hormone (GHRH), GRO-beta, GRO-beta antibody,bone morphogenic proteins such as bone morphogenic protein-2, bonemorphogenic protein-6, OP-1; acidic fibroblast growth factor, basicfibroblast growth factor, CD-40 ligand, heparin, human serum albumin,low molecular weight heparin (LMWH), interferons such as interferonalpha, interferon beta, interferon gamma, interferon omega, interferontau; interleukins and interleukin receptors such as interleukin-1receptor, interleukin-2, interluekin-2 fusion proteins, interleukin-1receptor antagonist, interleukin-3, interleukin-4, interleukin-4receptor, interleukin-6, interleukin-8, interleukin-12, interleukin-13receptor, interleukin-17 receptor; lactoferrin and lactoferrinfragments, luteinizing hormone releasing hormone (LHRH), insulin,pro-insulin, insulin analogues (e.g., mono-acylated insulin as describedin U.S. Pat. No. 5,922,675), amylin, C-peptide, somatostatin,somatostatin analogs including octreotide, vasopressin, folliclestimulating hormone (FSH), influenza vaccine, insulin-like growth factor(IGF), insulintropin, macrophage colony stimulating factor (M-CSF),plasminogen activators such as alteplase, urokinase, reteplase,streptokinase, pamiteplase, lanoteplase, and teneteplase; nerve growthfactor (NGF), osteoprotegerin, platelet-derived growth factor, tissuegrowth factors, transforming growth factor-1, vascular endothelialgrowth factor, leukemia inhibiting factor, keratinocyte growth factor(KGF), glial growth factor (GGF), T Cell receptors, CDmolecules/antigens, tumor necrosis factor (TNF), monocytechemoattractant protein-1 endothelial growth factors, parathyroidhormone (PTH), glucagon-like peptide, somatotropin, thymosin alpha 1,thymosin alpha 1 IIb/IIIa inhibitor, thymosin beta 10, thymosin beta 9,thymosin beta 4, alpha-1 antitrypsin, phosphodiesterase (PDE) compounds,VLA-4 (very late antigen-4), VLA-4 inhibitors, bisphosponates,respiratory syncytial virus antibody, cystic fibrosis transmembraneregulator (CFTR) gene, deoxyreibonuclease (Dnase),bactericidal/permeability increasing protein (BPI), and anti-CMVantibody. Exemplary monoclonal antibodies include etanercept (a dimericfusion protein consisting of the extracellular ligand-binding portion ofthe human 75 kD TNF receptor linked to the Fc portion of IgG1),abciximab, afeliomomab, basiliximab, daclizumab, infliximab, ibritumomabtiuexetan, mitumomab, muromonab-CD3, iodine 131 tositumomab conjugate,olizumab, rituximab, and trastuzumab (herceptin), amifostine,amiodarone, aminoglutethimide, amsacrine, anagrelide, anastrozole,asparaginase, anthracyclines, bexarotene, bicalutamide, bleomycin,buserelin, busulfan, cabergoline, capecitabine, carboplatin, carmustine,chlorambucin, cisplatin, cladribine, clodronate, cyclophosphamide,cyproterone, cytarabine, camptothecins, 13-cis retinoic acid, all transretinoic acid; dacarbazine, dactinomycin, daunorubicin, dexamethasone,diclofenac, diethylstilbestrol, docetaxel, doxorubicin, epirubicin,estramustine, etoposide, exemestane, fexofenadine, fludarabine,fludrocortisone, fluorouracil, fluoxymesterone, flutamide, gemcitabine,epinephrine, L-Dopa, hydroxyurea, idarubicin, ifosfamide, imatinib,irinotecan, itraconazole, goserelin, letrozole, leucovorin, levamisole,lomustine, mechlorethamine, medroxyprogesterone, megestrol, melphalan,mercaptopurine, methotrexate, metoclopramide, mitomycin, mitotane,mitoxantrone, naloxone, nicotine, nilutamide, octreotide, oxaliplatin,pamidronate, pentostatin, pilcamycin, porfimer, prednisone,procarbazine, prochlorperazine, ondansetron, raltitrexed, sirolimus,streptozocin, tacrolimus, tamoxifen, temozolomide, teniposide,testosterone, tetrahydrocannabinol, thalidomide, thioguanine, thiotepa,topotecan, tretinoin, valrubicin, vinblastine; vincristine, vindesine,vinorelbine, dolasetron, granisetron; formoterol, fluticasone,leuprolide, midazolam, alprazolam, amphotericin B, podophylotoxins,nucleoside antivirals, aroyl hydrazones, sumatriptan; macrolides such aserythromycin, oleandomycin, troleandomycin, roxithromycin,clarithromycin, davercin, azithromycin, flurithromycin, dirithromycin,josamycin, spiromycin, midecamycin, leucomycin, miocamycin, rokitamycin,andazithromycin, and swinolide A; fluoroquinolones such asciprofloxacin, ofloxacin, levofloxacin, trovafloxacin, alatrofloxacin,moxifloxicin, norfloxacin, enoxacin, grepafloxacin, gatifloxacin,lomefloxacin, sparfloxacin, temafloxacin, pefloxacin, amifloxacin,fleroxacin, tosufloxacin, prulifloxacin, irloxacin, pazufloxacin,clinafloxacin, and sitafloxacin; aminoglycosides such as gentamicin,netilmicin, paramecin, tobramycin, amikacin, kanamycin, neomycin, andstreptomycin, vancomycin, teicoplanin, rampolanin, mideplanin, colistin,daptomycin, gramicidin, colistimethate; polymixins such as polymixin B,capreomycin, bacitracin, penems; penicillins includingpenicllinase-sensitive agents like penicillin G, penicillin V;penicllinase-resistant agents like methicillin, oxacillin, cloxacillin,dicloxacillin, floxacillin, nafcillin; gram negative microorganismactive agents like ampicillin, amoxicillin, and hetacillin, cillin, andgalampicillin; antipseudomonal penicillins like carbenicillin,ticarcillin, azlocillin, mezlocillin, and piperacillin; cephalosporinslike cefpodoxime, cefprozil, ceftbuten, ceftizoxime, ceftriaxone,cephalothin, cephapirin, cephalexin, cephradrine, cefoxitin,cefamandole, cefazolin, cephaloridine, cefaclor, cefadroxil,cephaloglycin, cefuroxime, ceforanide, cefotaxime, cefatrizine,cephacetrile, cefepime, cefixime, cefonicid, cefoperazone, cefotetan,cefmetazole, ceftazidime, loracarbef, and moxalactam, monobactams likeaztreonam; and carbapenems such as imipenem, meropenem, pentamidineisethiouate, albuterol sulfate; lidocaine, metaproterenol sulfate,beclomethasone diprepionate, triamcinolone acetamide, budesonideacetonide, fluticasone, ipratropium bromide, flunisolide, cromolynsodium, and ergotamine tartrate; taxanes such as paclitaxel; SN-38, andtyrphostines.

The above exemplary biologically active agents are meant to encompass,where applicable, analogues, agonists, antagonists, inhibitors, isomers,and pharmaceutically acceptable salt forms thereof. In reference topeptides and proteins, the invention is intended to encompass synthetic,recombinant, native, glycosylated, non-glycosylated, and biologicallyactive fragments and analogs thereof.

The active substance may comprise two or more active substancesformulated together, such as one coated with another, or one dispersedwithin a matrix of another, or a physical mixture (blend) of two ormore. Common examples of such formulations include two or morecoformulated pharmaceutical actives, or pharmaceutically activesubstances coated with excipients, or physical mixtures ofpharmaceutically active substances with excipients such as in particularlactose, or solid dispersions of pharmaceutically active substances withexcipients, the excipient often being present to modify the release rateand/or to target delivery of the pharmaceutical. However, in general theactive substances of the invention will exhibit improved dispersibilityand DPI performance in the absence of excipients, ie, in the form of theactive substance alone (for example in the form of a drug or drugswithout excipients).

The improved dispersibility and DPI performance is preferably alsoexhibited in the absence of dispersion-enhancing or stabilisingadditives, such as surfactants or lubricants.

Preferably a particulate active substance according to the inventionwill exhibit improved dispersibility and DPI performance as compared tothe same active substance, in particulate form, prepared by a non-SEDS™particle formation process, in particular micronisation or granulation.By “micronisation” is meant a process involving mechanical means, forinstance milling or grinding, to reduce particle size to the micrometerrange. The non-SEDS™ substance may comprise particles having the same ora smaller size (for instance, 90% or less of the size of, or preferably80% or 70% or 60% or less of the size) than those of the activesubstance of the invention.

In certain cases, an active substance according to the present inventionmay be a pharmaceutically active substance or a pharmaceuticallyacceptable excipient (preferably a substance suitable for and/orintended for delivery by inhalation) other than salmeterol xinafoate(alone or coformulated with hydroxypropyl cellulose); α-lactosemonohydrate; R-TEM β-lactamase; maltose; trehalose; sucrose; budesonide;salbutamol sulphate; nicotinic acid; paracetamol (alone or coformulatedwith salmeterol xinafoate, L-poly(lactic acid), ethyl cellulose (EC),hydroxypropyl methyl cellulose (HPMC) or poly vinyl pyrrolidone (PVP));ibuprofen; ketoprofen (alone or coformulated with EC, HPMC or PVP);salicylic acid; either indomethacin, carbamazepine, theophylline,ascorbic acid or a COX-2 selective inhibitor coformulated with EC, HPMCor PVP; quinine sulphate coformulated with EC; fluticasone propionate;omeprazole magnesium tetrahydrate; (S)-omeprazole magnesium trihydrate;formoterol fumarate dihydrate; felodipine; candesartan cilexetil;lysozyme; albumin; insulin; terbutaline sulphate; fenoterolhydrobromide; dihydroergotamine mesylate; and/orrisperidone-(9-hydroxy)-palmitate.

It has been found that particulate active substances which exhibit theimproved DPI performance and other advantageous properties describedabove can be produced using the so-called SEDS™ (“Solution EnhancedDispersion by Supercritical fluid”) process, which is a version of theGAS process referred to above.

SEDS™ is a process for forming particles of a “target” substance. Itinvolves contacting a solution or suspension of the target substance ina fluid vehicle (the “target solution/suspension”) with an excess of acompressed fluid (generally a supercritical or near-critical fluid)anti-solvent under conditions which allow the anti-solvent to extractthe vehicle from the target solution/suspension and to cause particlesof the target substance to precipitate from it. The conditions are suchthat the fluid mixture thus formed between the anti-solvent and theextracted vehicle is still in a compressed or supercritical ornear-critical state. The anti-solvent fluid should be a nonsolvent forthe target substance and be miscible with the fluid vehicle.

Carrying out a SEDS™ process specifically involves using theanti-solvent fluid simultaneously both to extract the vehicle from, andto disperse, the target solution/suspension. In other words, the fluidsare contacted with one another in such a manner that the mechanical(kinetic) energy of the anti-solvent can act to disperse the targetsolution/suspension at the same time as it extracts the vehicle.“Disperse” in this context refers generally to the transfer of kineticenergy from one fluid to another, usually implying the formation ofdroplets, or of other analogous fluid elements, of the fluid to whichthe kinetic energy is transferred.

Suitable SEDS™ processes are described in WO-95/01221 WO-96/00610,WO-98/36825, WO-99/44733 and WO-99/59710, WO-01/03821 and WO-01/15664,in our co-pending PCT patent application no. PCT/GB PCT/GB01/04873 andin our co-pending UK patent application no. 0117696.5. Other suitableSEDS™ processes are described in WO-99/52507, WO-99/52550, WO-00/30612,WO-00/30613 and WO-00/67892, all of which are hereby incorporated intheir entirety by reference.

In SEDS™, the target solution/suspension and the anti-solvent arepreferably contacted with one another in the manner described inWO-95/01221 and/or WO-96/00610, being co-introduced into a particleformation vessel using a fluid inlet means which allows the mechanicalenergy (typically the shearing action) of the anti-solvent flow tofacilitate intimate mixing and dispersion of the fluids at the pointwhere they meet. The target solution/suspension and the anti-solventpreferably meet and enter the particle formation vessel at substantiallythe same point, for instance via separate passages of a multi-passagecoaxial nozzle.

A particulate active substance according to the first aspect of thepresent invention is preferably prepared using a SEDS™ process, such asone or a combination of those described in the above documents.Preferred features of the process may be as described below inconnection with the fourth aspect of the invention. The active substancemay thus be insoluble or only sparingly soluble in water. It ispreferably insoluble or only sparingly soluble in compressed (eg,supercritical or near-critical) carbon dioxide. Such materials lendthemselves particularly well to SEDS™ processing and indeed are oftendifficult to process using other particle formation techniques such asspray drying or freeze drying.

Thus, a fourth aspect of the present invention provides the use of aSEDS™ process (as described above) to produce an active substance inparticulate form, for the purpose of improving the dispersibility of thesubstance and/or its performance in a passive dry powder deliverydevice, and/or for the purpose of achieving one or more of thecharacteristics (a) to (q), optionally in combination with one or moreof the other preferred properties, listed above in connection with thefirst aspect of the invention.

The process is preferably carried out using supercritical ornear-critical, more preferably supercritical, CO₂ as the anti-solvent.The choice of operating conditions such as temperature, pressure andfluid flow rates, and the choice of solvent and of anti-solvent modifierif necessary, will depend on the nature of the active substance, forinstance its solubility in the fluids present and, if it can exist indifferent polymorphic forms, which form is to be precipitated.Generally, the conditions should be chosen to minimise or reduceparticle sizes and/or size distributions—this will generally meanselecting a higher anti-solvent flow rate (eg, a targetsolution/suspension: anti-solvent flow rate ratio (at or immediatelyprior to the two fluids coming into contact with one another) of 0.03 orless, preferably 0.02 or less or even 0.01 or less), and/or a higheroperating temperature (eg, from 50 to 100° C., preferably from 70 to 90°C., especially for a CO₂ anti-solvent), and/or a higher operatingpressure (eg, from 80 to 210 bar, preferably from 90 to 200 bar, againespecially for a CO₂ anti-solvent).

The process conditions are also ideally chosen to maximise or enhancethe purity (which may be the polymorphic or enantiomeric purity) of theproduct—this will involve the use of a vehicle, anti-solvent,temperature and pressure suitable to maximise or enhance selectivity ofprecipitation of the desired substance from those present in the targetsolution/suspension.

The operating conditions for the process (in particular the targetsolution/suspension concentration and the relative flow rates of thetarget solution/suspension and anti-solvent) are preferably selected,for any particular set of reagents (including the fluid vehicle andanti-solvent) and particle formation vessel and fluid inlet geometry, soas to maximise or enhance the degree of supersaturation in the targetsolution/suspension flow at its point of contact with the anti-solvent.This may be effected for instance in the manner described in theexamples below, using solubility measurements to determine the optimumoperating conditions.

The product of the fourth aspect of the invention is preferably aparticulate active substance according to the first aspect.

Improving the performance of a substance in a passive dry powderdelivery device will typically mean increasing the fine particlefraction in the emitted dose when the active substance is deliveredusing a passive dry powder inhaler. The improvement may for instance beas compared to the performance of the substance prior to the SEDS™processing, and/or of the same substance (preferably having the sameparticle size or a particle size no more than 10% or 20% or 30% or 40%different) when produced using another particle formation process suchas micronising, granulation or conventional spray drying.

According to a fifth aspect of the present invention, there is providedan active substance for use in a method of surgery, therapy or diagnosispractised on a human or animal body, in which method the substance isdelivered to a patient using a passive dry powder inhaler or analogousdelivery device, wherein the substance has one or more of the propertiesdescribed above in connection with the first to the fourth aspects ofthe invention.

A sixth aspect of the invention provides the use of an active substancein the manufacture of a medicament for use in a passive dry powderinhaler or analogous delivery device, wherein the substance has one ormore of the properties described above in connection with the first tothe fourth aspects of the invention.

For the fifth and sixth aspects of the invention, the active substanceis preferably an active substance according to the first aspect, and ispreferably prepared using the method of the fourth aspect and/orselected using the method of the second aspect. It is preferably apharmaceutically or nutriceutically active substance. Other preferredfeatures of the fifth and sixth aspects of the invention may be asdescribed in connection with the first to the fourth aspects.

A seventh aspect of the present invention provides a dosage formulationor collection thereof, for use in a drug delivery device such as inparticular a dry powder inhaler, the dosage formulation containing aparticulate active substance according to the first aspect of theinvention. Preferably the formulation consists essentially of the activesubstance, ie, it contains 95% w/w, preferably 98% w/w or 99% w/w, ormore of the active substance. In particular, it may consist essentiallyof a pharmaceutically active substance in the absence of excipientsand/or of dispersion enhancing or stabilising additives.

An eighth aspect of the invention provides an active substance (eg,drug) delivery device, preferably an inhaler, which contains one or moredosage formulations of an active substance according to the firstaspect. The delivery device is preferably of the type designed todeliver a predetermined dose of an active substance in a dry (ie,without a fluid carrier) particulate form, for instance a dry powderinhaler and in particular a passive dry powder inhaler. It may containone or more dosage formulations according to the seventh aspect of theinvention.

According to a ninth aspect, the invention provides a method fordelivering an active substance, the method involving charging a deliverydevice, in particular a device according to the eighth aspect of theinvention, with an active substance and/or a formulation according tothe invention and/or an active substance selected in accordance with thesecond aspect of the invention.

A tenth aspect provides a method of treatment of a human or animalpatient, which method involves administering to the patient, preferablyusing the method of the ninth aspect of the invention, an activesubstance and/or a formulation according to the invention and/or anactive substance selected in accordance with the second aspect of theinvention.

Both of these methods preferably involve the use of a delivery devicesuch as an inhaler, more preferably a delivery device according to theeighth aspect of the invention. The active substance preferablycomprises a pharmaceutically active substance suitable for inhalationtherapy.

The present invention will now be illustrated with reference to thefollowing examples, which show how a SEDS™ process may be used toprepare particulate active substances with advantageous properties foruse in passive dry powder inhalers.

EXAMPLES

The system used to carry out the SEDS™ particle formation processes wasof the general type shown schematically in the figures of WO-95/01221.

Example 1

The SEDS™ method described in WO 95/01221 was employed to preparepowders of salmeterol xinafoate (SX, GlaxoSmithKline), terbutalinesulphate (TBS, AstraZeneca) and fenoterol hydrobromide (FHBr, BoehringerIngelheim). The particle formation vessel of 0.5 L volume was used inall cases. Several solvents including methanol. Ethanol, acetone andtetrahydrofurane were tested. Typical flow rate of CO₂ was 5 kg/hour.

Analytical Methods PSD measurements were performed using firstly,AeroSizer time-of-flight instrument equipped with AeroDisperser™ (TSIInc., Minneapolis. USA) and secondly, laser diffraction sensor Heloswith dry-powder air-dispersion system Rodos (Sympatec GmbH. Germany).The volume mean particle diameter, VMD, was obtained for bothinstruments using software options. In the general case of non-sphericalparticles, these instruments cannot provide the exact value of VMD,however, the time-of-flight technique gives an aerodynamic-equivalentparticle diameter, whereas the laser diffraction method provides thegeometric projection-equivalent diameter. These diameters afford thecomplementary information on PSD and therefore can be used forcomparative size analysis.

For SX powders, inverse gas chromatography (IGC) was performed using aHewlett Packard Series 5890 Gas Chromatograph equipped with anintegrator and flame ionization detector. For TBS and FHBr powders, IGCwas done using a Hewlett Packard Series 6890 instrument which wasspecifically modified for IGC measurements by Surface MeasurementSystems Ltd (Manchester, UK). The IGC method is described in detail byTong et al. 2001. (Tong H. H. Y., B. Y. Shekunov, P. York, A. H. L.Chow, 2001. Pharm. Res. 18, 852.) Triplicate measurements in separatepacked columns were made. Differences in surface energetics werereflected in the calculated dispersive component of the surface freeenergy, γ_(S) ^(D), specific component of surface free energies ofadsorption. ΔG_(A); the acid-base parameters, K_(A) and K_(O) and thetotal (Hildebrand) solubility parameter, δ, which reflects the adhesionwork between particles. The γ_(S) ^(D) and ΔG_(A) values were obtainedat 303K.

The deposition behaviour of micronised and supercritically-producedpowders were evaluated using an Andersen-type cascade impactor (CopleyScientific Limited, Nottingham. UK). This device is designed to imitateparticle deposition in the lungs; the control criterion is that the highfine particle fraction (FPF) of a respirable drug to be delivered to thedefined stages (from 1 to 5) of the cascade impactor. The drugs wereblended with inhalation grade, DMV Pharmatose® 325M α-lactosemonohydrate, with 3.8% w/w of drug typical for such formulation. Theairflow through the apparatus measured at the inlet to the throat, wasadjusted to produce a pressure drop of 4 kPa over the inhaler under test(Clickhaler™) according to compendial guidelines, consistent with theflow rate 49 L/min.

Several batches of particulate material of respirable size withcumulative PSD for all batches X₉₉<10 μm were consistently prepared,with batch quantities between 1 and 10 g. VMD of powders obtained usingdifferent techniques are shown in Table 1.

TABLE 1 VMD (μm) VMD (μm) Compound (Time of flight) (laser diffraction)FPF (%) SX Micronised 1.2 1.69 25.1 SX SEDS 1.6 3.56 57.8 TSB Micronised2.7 3.04 30.7 TSB SEDS 3.4 3.43 38.6 FHBr Micronised 1.7 2.34 17.4 FHBrSEDS 1.7 3.55 41.7

These data indicate that although both the aerodynamic (time of flight)and geometric (laser diffraction) diameters for the micronised paniclesare smaller than the correspondent VMD for supercritically-producedmaterials, the FPF deposited in the cascade impactor is significantlylarger for the supercritically-produced powders. Therefore the powderdispersion rather than the particle size distribution defines thedeposition profile of the drug particles in this aerosol test.Dispersability of powders in the air flow is defined by the balance offorces generated by the aerodynamic stresses and the inter-particulateforces. The theoretical tensile strength of the particle aggregate,required to separate primary particles, is proportional to the work ofparticle adhesion (Kendell and Stainton, 2001) and can be associatedwith the specific surface energy defined by the IGC method. Table 2represents the surface-energy related parameters which reflect theinteraction of the non-polar γ_(S) ^(D) and polar ΔG_(A) nature.

TABLE 2 ΔG_(A) (kJ/mol) γs^(D) Diethyl Tolu- Ace- Ethyl Chloro- Diox-Substance (mJ/m²) ether ene tone acetate form ane SX 40.49 14.20 15.2417.46 14.78 Micron- ised SX SEDS 34.55 12.65 (0.08) (0.06) (0.24) TSB58.61 3.42 12.57 16.01 1.79 15.96 Micron- ised TSB 55.05 2.85 10.4213.76 1.21 14.20 SEDS FHBr 48.53 4.77 0.69 Micron- ised FHBr 49.87 3.8613.15 17.48 0.63 15.32 SEDS

The reduced magnitude of γ_(S) ^(D) for the supercritically-producedpowders implies that the surfaces of these particles are less energeticfor non-polar, dispersive surface interactions than the micronisedmaterials. The largest changes are however observed for the polarinteractions ΔG_(A) which are significantly smaller, by a factor of 1.5on average, for the supercritically-produced powders. In general, theenhanced powder dispersion always correlated well with the reducedsurface energy of these materials.

Example 2

Salmeterol xinafoate (SX) (GlaxoWellcome, Ware UK) in the form ofgranulated material (G-SX) used for micronisation and micronised powder(M-SX). HPLC grade solvent was purchased from BDH Chemicals, Leicester,UK. All analytical grade liquid probes used in IGC studies werepurchased from Labscan. Dublin, Ireland. Industrial grade (>99.95% pure)CO₂ was supplied by Air Products (Manchester, UK).

The SEDS™ method was employed to prepare powders of SX form I (S-SX).This technique is based on mixing between supercritical CO2 antisolventand a drug solution using a twin-fluid nozzle as more fully described inWO 95/01221 cited above. Methanol, acetone and tetrahydrofurane weretested in this work. The particle formation vessel (500 ml volume) withthe nozzle was placed in an air-heated oven. The temperature in thevessel was monitored by a thermocouple with accuracy ±0.1° C. and waskept constant at 40° C. Pressure in the vessel was controlled by anair-actuated back-pressure regulator (26-1761 with ER3000 electroniccontroller, Tescom. Elk River, Minn., USA) and kept constant at 250±1bar. The difference in the inlet and outlet pressure was typicallywithin 1% of its absolute value. The CO2 flow rate, supplied by awater-cooled diaphragm pump Milton Roy B (Dosapro Milton Roy,Pont-Saint-Pierre, France) was typically between 25 and 50 NL/min asmonitored after expansion using a gas flow meter (SHO-Meter 1355, BrooksInstruments B. V., Veenendal, Holland) and also controlled beforeexpansion using high-pressure liquid flow meter (DK34, KrohmeMesstechnik GmbH, Duisburg, Germany). Solution concentration of SXvaried between 1 and 10% w/v. Solution flow rate was provided by ametering pump PU-980 (Jasco Co, Tokyo, Japan) and varied from 0.5 to 10ml/min.

Several batches were prepared with batch quantities between 1 and 10 g.The obtained cumulative PSD for all batches had X₉₀≈10 μm andvolume-moment mean particle diameter, d_(4,3)≈5 μm, as determined usingthe laser diffraction (LD) method.

Inverse gas chromatography (IGC) was performed on a Hewlett PackardSeries II 5890 Gas) Chromatograph (Hewlett Packard, Wilmington, Del.,USA) equipped with an integrator and flame ionization detector. Injectorand detector temperatures were maintained at 100 and 150° C.respectively. Glass columns (60 cm long and 3.5 mm i.d.) weredeactivated with 5% solution of dimethyldichlorosilane in toluene beforebeing packed with SX powder. The columns were plugged with silanisedglass wool at both ends and maintained at 40° C. Data were obtained fora known weight and surface area of the sample using a nitrogen gas(purity>99.995%) flow at 20.0 ml/mm. The column was weighed before andafter the experiment to ensure no loss of materials during the run.Trace amount of vapour from non-polar and polar probes was injected. Theretention times and volumes of the injected probes were measured atinfinite dilution and thus were independent of the quantity of probesinjected. The non-polar probes employed were pentane, hexane, heptane,octane and nonane: the polar probes were dichloromethane, chloroform,acetone, ethyl acetate, tetrahydrofuran and diethyl ether. Triplicatemeasurements in separate columns were made for G-SX. M-SX and S-SXpowders. Differences in surface energetics were reflected in thecalculated dispersive component of the surface free energy, γ_(S) ^(D);specific component of surface free energies of adsorption, −ΔG_(A)^(SP), and the acid-base parameters, K_(A), and K_(D).

Data on specific surface areas required for IGC studies were determinedby BET nitrogen adsorption using a Surface Area Analyzer Coulter SA 3100(Coulter Corp., Miami, Fla., USA). Samples were placed in glass sampleholders and out-gassed with helium (purity>99.999%) at 40° C. for 16hours before analysis. Nitrogen (purity>99.999%) was used as adsorbateand BET surface area was recorded as specific surface area of thesamples. All measurements were performed in triplicate using the samebatch of each material.

Electric Charge and Adhesion Measurements

Triboelectrification was undertaken against a stainless steel contactsurface using either a turbula mixer or a cyclone separator.Triboelectrification in a turbula mixer (Glen Creston, UK) was carriedout by agitating a powder sample for 5 minutes at 30 rpm in a 100 mlstainless steel vessel at ambient temperature and relative humidity. Asample was poured in a reproducible manner into a Faraday well connectedto an electrometer (Keithley 610, Keithley Instruments, Reading, UK).Charge and mass of sample was then recorded to give specific chargebefore and after triboelectrification. % w/w adhesion to the innersurface of the mixing vessel was calculated from the original mass ofsample and the mass of sample poured into the Faraday well. Duringtriboelectrification in a cyclone separator, a powder was fed from asteel vibratory table into a venturi funnel. Compressed air (velocity 8m/s. relative humidity below 10%, ambient temperature) was used toconvey the powder from the venturi along a horizontal pipe into thecyclone separator. The Faraday well and force compensation load cell wasfitted at the base of the cyclone and used to collect charged particles.Final specific charge was recorded for non-adhered powder residing inthe Faraday well and, where possible, powder adhering to the cyclonewall was dislodged by a stream of air and its charge and mass recorded.In both cases, the results were obtained from triplicate measurements.

Particle Size Analysis

The instrument consisted of laser diffraction sensor HELOS anddry-powder air-dispersion system RODOS (Sympatec GmbH. Germany) withWINDOX OS computer interface. The dispersion process was controlled bymeans of adjusting pressure of the compressed air flow between 0.5 and 5bar. The pressure of 2 bar was found to be sufficient to disperse mostof the agglomerates avoiding, at the same time, attrition of the primaryparticles. All measurements were performed in triplicate. The particleshape factor, f, was calculated asf=Sv/Sv*. where Sv is the experimentalspecific surface area and Sv* is the specific surface area determinedusing the LD instrument assuming the particle sphericity.

Results and Discussion: Surface Free Energy and Specific Surface Area

The fundamental quantity of inverse gas chromatography is the netretention volume, V_(N), determined from the retention time of a givensolvent. Adsorption of the probe molecules on solid surfaces-can beconsidered in terms of both dispersive and specific components ofsurface free energy, corresponding to non-polar and polar properties ofthe surface. By virtue of their chemical nature, non-polar probes of thealkane series only have dispersive component of surface free energy,which can be determined from the slope of the plot based the followingequation:RTInV _(N)=2aN _(A)(γ_(S) ^(D))^(1/2)(γ_(L) ^(D))^(1/2)+const

where R is the gas constant. T is the column's absolute temperature, ais the probe's surface area. N_(A) is the Avogadro's number, γ_(S) ^(D)is the dispersive component of surface free energy of a SX powder andγ_(L) ^(D) is the dispersive component of surface free energy of thesolvent probes. Polar probes have both dispersive and specificcomponents of surface free energy of adsorption. The specific componentof surface free energy of adsorption (ΔG_(A) ^(SP)) can be estimatedfrom the vertical distance between the alkane reference line and thepolar probes of interest. This free energy term can be related to thedonor number (DN) and acceptor number (AN*) of the polar solvent by thefollowing equation:ΔG _(A) ^(SP) =K _(A) DN+K _(D) AN*

DN describes the basicity or electron donor ability of a probe whilstAN* defines the acidity or electron acceptor ability. Here, AN* denotesa correction for the contribution of the dispersive component and theentropy contribution into the surface energy is assumed negligible. Thusplotting −ΔG_(A) ^(SP)/AN* versus DN/AN* yields a straight line whereK_(A) and K_(D) correspond to the slope and intercept respectively.

The IGC data for the various SX samples analysed by the above approachare summarized in Tables 3 and 4. Comparison between different materialsshows that the magnitude of γ_(S) ^(D) is 15% smaller for S-SX compoundsthan for both M-SX and G-SX compounds. In addition, ΔG_(A) ^(SP) for allpolar probes used reduced by at least half for S-SX compound compared tothe other two materials. Comparison between M-SX and G-SX materialsindicates that, although the γ_(S) ^(D) are almost equal within theexperimental error, ΔG_(A) ^(SP) for all the polar probes is larger forthe granulated material. The specific surface area, a, is twice as smallfor the S-SX compound compared with both M-SX and G-SX materialsindicating that the mean surface-equivalent particle diameter for thesecompounds is smaller than for S-SX compound.

The reduced magnitude of γ_(S) ^(D) for S-SX compound implies that thesurfaces of these panicles are less energetic for non-polar, dispersivesurface interactions than the other two compounds. The overall strengthof the polar interactions ΔG_(A) ^(SP) is also the smallest for S-SXcompound. Comparison between the K_(A) and K_(D) values of the threesamples indicate that the acidity constant has the following trend:K_(A)(S-SX)<K_(A)(M-SX)<K_(A)(G-SX). The basicity constants follows thereverse order with K_(D)(S-SX) being the largest. Thus S-SX sample whichhas the weakest acidic property exhibits the strongest basicinteractions with respect to its exposed polar groups at the interface.This suggests that S-SX crystal surfaces have, in relative terms, moreexposed basic groups but fewer exposed acidic groups than both G-SX andM-SX compounds. Particles of all three compounds have a similar plateletshape with the dominant {101} crystal faces. However, S-SX particleshave the largest shape factor, f(see Table 3), which means thatplatelets of G-SX and M-SX are thicker. The other materials have moreenergetic lateral crystal surfaces as a result of the solutioncrystallisation procedure (G-SX) and particle breakage on micronisation(M-SX). Therefore the observed differences in K_(A) and K_(D), combinedwith the smallest magnitude of ΔG_(A) ^(SP) and γ_(S) ^(D) for S-SXcompound, suggests a combination of three different factors affectingthe specific surface energy: (a) difference in the crystal habit. i.e.the {001} crystal faces have stronger basic and weaker acidicinteractions than the lateral crystal faces, (b) smaller overallspecific surface energy of the {001} crystal planes as compared to anyother crystallographic planes and (c) disturbances of the crystalstructure which also contribute to the higher surface energy of G-SX andM-SX compounds.

It is clear that solvent adsorption-progress more rapidly with the M-SXand G-SX samples than with S-SX material. This fact indicates thatsupercritical fluid process of the invention produces particles withlower surface activity (and greater surface stability) than powdersproduced by solution crystallisation and micronisation.

TABLE 3 Compound γ_(S) ^(D) (mJ/m²) K_(A) K_(D) S_(V) f S-SX 32.4760.110 0.356 7.040 3.78 M-SX 38.285 0.172 0.298 9.243 2.80 G-SX 36.9720.233 0.157 10.699 —

TABLE 4 −ΔG_(A) ^(SP) (kJ/mol) Dichloro- Chloro- Ethyl Diethyl Tetrahy-methane form Acetone acetate ether drofuran S-SX 2.308 0.153 3.797 2.7051.488 2.446 M-SX — 0.810 4.560 3.995 2.774 3.609 G-SX — 1.885 5.4544.739 2.958 4.854

Table 5 presents results on the charge, Q, and fraction of adheredmaterial, AD. S-SX particles exhibited significantly less (between oneand two orders of magnitude) accumulated charge than the micronisedpowder before and after turbula mixing and also for the non-adhered drugin cyclone separator. Correspondingly, the fraction of adhered materialis several times smaller for S-SX powder than for M-SX powder in boththe turbula mixing and cyclone separator tests.

These results are consistent with the superior powder flow properties ofS-SX material. Although the bulk powder density of S-SX material is verylow (about 0.1 g/cm⁻¹ vs. 0.5 g/cm³ for M-SX) it flows well and does notadhere to the container walls.

TABLE 5 Turbula Mixer Cyclone Separator Q (nCg⁻¹) Q (nCg⁻¹) AD Q (nCg⁻¹)Q (nCg⁻¹) AD Before After (% Before After (% mixing mixing w/w) mixingmixing w/w) S-SX −0.52 −0.17 1.5 4.9 −34.6 5.5 M-SX −12.1 −42.6 27 −48.4−49.7 16.7

Particle Size and Powder Dispersability

The difference in PSD of S-SX and M-SX powders is reflected in themagnitude of the mean particle sizes d_(4,3)=3.5 μm (S-SX) and 1.8 μm(M-SX) and as measured using the LD technique. For both materials thecumulative PSD>98% within respirable particle size range 0.5<x<10 μm.However, a significant difference was observed between the dispersionbehavior of micronised and supercritically-process-ed powders. At highdispersing pressures above≈2 bar, d_(4,3) is smaller for M-SX powder, asindicated by the primary PSD for this compound. This situation changesdramatically at dispersing pressures below 2 bar. At low pressures, S-SXpowders consistently produce a large fraction of primary particles inthe respiratory size range, whereas M-SX powders form stableagglomerates outside the 5 μm range which cannot be dispersed at suchpressures.

The enhanced dispersability of S-SX powders-means a decrease of theinter-particulate contact area and/or reduction of the cohesive forcesleading to better performance of S-SX compound in the inhalationdevices. Despite a larger geometric (and volume) diameter for S-SXparticles, the Andersen cascade impactor measurements indicated agreater than two-fold increase (from 25.15 to 57.80%) of FPF for S-SXpowder compared with FPF of M-SX powder.

Example 3

This example measured the surface charge and adhesiveness of particlesof the drug salbutamol sulphate produced using a SEDS™ process ascompared to that of both the unprocessed starting material and amicronised sample of the drug.

Surface charge was examined by placing weighed portions of the samplesin a Faraday well to measure their electrostatic charge.

A simple adhesion test was devised to examine the observation that theultra-fine powders prepared by the SEDS™ process exhibited low adhesionto containers and vessel walls, and low adhesive interaction withsurfaces in general. In this test, a small quantity of powder wasweighed into a screw topped glass jar and the jar rotated for 5 minutes.The non-adhering powder was then tipped from the jar and weighed and thepercentage powder adhering to the walls of the jar calculated.

The results of both the charge and the adhesion tests are shown in Table6 below. It can be seen that both the unprocessed and the micronisedmaterials exhibited relatively high surface charge, whilst the figurefor the SEDS™ sample was dramatically reduced. Further, in the adhesiontests, there was minimal adhesion of the SEDS™ processed material,whilst significant amounts of the micronised form of the same materialadhered to the surfaces of the jar.

These findings are consistent with the surprisingly observed easyflowing nature of SEDS™ products, being different from the generallyobserved highly charged, cohesive and non-free flowing nature ofmicronised materials of a similar particle size.

TABLE 6 Relative Powder Adhesion Sample Electrostatic Charge (nC/g) (tocontainer walls) Unprocessed −23.1 8.6 Micronised −42.6 18.6 SEDS −0.21.0

Example 4

This example measured the specific surface area (by low temperaturephysical adsorption of nitrogen) of a poorly aqueous soluble drugproduced using a SEDS™ process, as compared to a micronised sample ofthe same drug.

The specific surface area of the micronised sample was 5.6 m²/g, whereasthat of the SEDS™ sample was 27.8 m²/g.

Example 5

These examples assessed the dissolution performance of an aqueoussoluble compound produced using a SEDS™ process and also in a micronisedform. A conventional test method was used, as described in the currentpharmacopoeia and compendia (eg, BP and USP). Three SEDS™-producedsamples were tested.

The results are shown in FIG. 1, which plots the percentage dissolutionagainst time. The ultra-fine particulate products of the inventionclearly dissolves much more rapidly and efficiently than the micronisedversion of the same substance, exhibiting much faster dissolutionprofiles to complete dissolution. A further advantage of the SEDS™products is the consistency of their dissolution profiles between repeatbatches.

Example 6

These examples assessed the surface roughness of a SEDS™-producedmaterial as compared to that of (a) the crystallised starting materialand (b) the same compound in a micronised form. Conventional AFManalysis was used for the assessments.

The results are shown in FIGS. 2 (AFM analysis of the SEDS™-processedmaterial) and 3 (graph showing RMS surface roughness data for the threesamples) below. The SEDS™ sample clearly had a smoother topographicalcharacter.

Example 7

The properties of a micronised sample of salbutamol sulphate werecompared with those of a SEDS™-processed sample of the same drug. TheSEDS™ sample was prepared from a 10% w/v solution of salbutamol sulphatein acetone, using a 568 ml particle formation vessel, a two-passageconcentric nozzle with a 0.1 mm internal diameter orifice, a processingtemperature of 50° C., and pressure of 150 bar, a drug solution flowrate of 0.04 ml/min and a supercritical carbon dioxide anti-solventflowing at 18 ml/min.

The mean amorphous content of the micronised sample, determined by thedynamic moisture sorption method, was 6.92%, w/w (standard deviation1.10). That of the SEDS™ sample in contrast was only 0.13% w/w (SD0.05).

The mean value for γ_(S) ^(D) (the dispersive component of surface freeenergy, determined by IGC) was 58.57 mJm⁻² (SD 2.19) for the micronisedsample but only 38.45 mJm⁻² (SD 1.50) for the SEDS™ sample.

The mean specific charge of both samples was +4.00 nCg⁻¹ before mixing.After triboelectrification by Turbula™ mixing this value had increasedto +25.9 nCg⁻¹ for the micronised sample but only +16.4 nCg⁻¹ for theSEDS™-produced sample.

Further, blends of salbutamol sulphate with lactose (both a micronisedand a SEDS™-produced sample) were tested in an Andersen-type cascadeimpactor with a Clickhaler™ DPI device. The fine particle fraction ofthe emitted dose was measured as 11.86% for the micronised sample and33.57% for the SEDS™ one.

Example 8

The respiratory drug terbutaline suplphate (TBS) was prepared by SEDS™process and its properties and DPI performance compared to those of amicronised sample of the same drug. The DPI performance of blends of TBSwith the carrier alpha-lactose monohydrate was also investigated, sincethe drug-carrier adhesion and hence the particulate (especially surface)properties of the drug and carrier; can significantly influence theirdispersibilty in DPI systems.

Production of Powers

Materials

The material studied was supplied as solution (2% w/v) was delivered bya separate reciprocating HPLC pump (Jasco PU-980, Japan) and variedbetween 0.1 and 4.8 ml/min. Liquid CO₂ (−10° C.,) was pumped by awater-cooled Dosapro Milton Roy pump (Type: MB 112S (L) 10M 480/J VV2,Pont-Saint-Pierre, France) and flow was varied between 4.5 and 80 ml/mm.The CO₂ passed through a heat exchanger to ensure that it wassupercritical before entering the nozzle, which consisted of twoconcentric tubes and a small premixing chamber. Two nozzle diameters,0.1 and 0.2 mm were used in the study. The powder (typically about 200mg a batch) was collected from the vessel and analysed. A range ofoperating temperatures (35-80° C.) and pressures (80-250 bar) wereapplied to produce drug powder using the SEDS™ process.

Physical Characterisation of Powders

Particle Size Analysis

Laser Diffraction

A small amount of TBS powder was analysed using a laser diffractionRODOS/VIBRI dispersing system (HELOS/RODOS, Sympatec GmbH,Clausthal-Zellerfeld, Germany). The instrument consisted of a lasersensor HELOS and a RODOS dry-powder air-dispersion system (SympatecGmbH, Clausthal-Zellerfeld, Germany). Different measurement ranges ofthe laser sensor were provided by interchangeable objectives R1 (0.1-35μm) and R2 (0.25-87.5 μm). The rate of powder dispersion was controlledby adjusting the pressure of the compressed air flow. A pressure of 2bar was sufficient to achieve deagglomeration of primary particleswithout attrition.

Time-of-Flight Measurements

The TBS samples were also analysed using an AeroSizer™ (Amherst ProcessInstruments, Amherst, Mass., USA), provided with pulse jet disperser,the AeroDisperser™, to introduce the powders to the instrument. The wereanalysed for 300 seconds in triplicate using normal deagglomerationconditions, feed rate (5000 particles per second) and medium shear force(0.5 psi).

micronised powder of terbutaline sulphate (AstraZeneca R & D, Lund,Sweden), α-lactose monohydrate (Pharmatose 325 M inhalation grade DMVInternational, Veghel, The Netherlands) was used as a carrier for thecascade impaction studies. Carbon dioxide (BOC Ltd, UK) was 99.9% pureand methanol, ethanol and water were of HPLC grade (Fischer ScientificLimited, Loughborough, UK). Chloroform, toluene, ethyl acetate, acetoneand 1,4-dioxane, of HPLC grade (99+% purity) were used as polar probeswhereas a series of n-alkanes from hexane (n=6) to decane (n=10) of HPLCgrade (99+% purity) were used as non-polar probes for IGC analysis.

Solution Enhanced Dispersion by Supercritical Fluids (SEDS™) Process

For experiments that used ethanol as a solvent, the SEDS™ process wasmodified in such a way that an additional extraction vessel packed withTBS powder was placed in an oven and pure ethanol was pumped through thevessel. This enhanced extraction of TBS and resulted in productyield >85% w/w (see FIG. 4, vessel position indicated by dotted lines).All other experiments were conducted in a SEDS™ apparatus as disclosedin WO 95/01221 consisting of a stainless steel particle formation vessel(50 ml) positioned in an air assisted heated oven with a speciallydesigned two flow coaxial nozzle capable of withstanding a pressure of500 bar. Pressure in the system was maintained within ±1 bar by anautomated back-pressure regulator (Tescom, Japan). Drug

Scanning Electron Microscopy (SEM)

A small amount of powder was manually dispersed onto a carbon tabadhered to an aluminium stub, (Agar Scientific, UK). The sample stubswere coated with a thin layer (200 Å) of gold by employing an EmitechK550 sputter coater (Texas, USA). The samples were examined by SEM(Hitachi S-520, Tokyo, Japan) and photographed under variousmagnifications with direct data capture of the images onto a personalcomputer.

Solid State Analysis

X-Ray Powder Diffraction (XRPD)

Structural analysis of the samples was performed using an X-ray powderdiffractometer (Siemens, D5000, Karlsruhe, Germany), fitted with arotating sample holder, a scintillation counter detector and a divergentbeam utilising a CuKα source of X-rays (λ=1.5418 Å). Each sample wasplaced in the cavity of an aluminium sample holder flattened with aglass slide to present a good surface texture and inserted into thesample holder. In order to measure the powder pattern, the sample holderand detector were moved in a circular path to determine the angles ofscattered radiation and to reduce preferred sample orientation. Allsamples were measured in the 2θ angle range between 1.5° and 45° with ascan rate of 3 seconds/step and a step size of 0.05°. Samples wereanalysed in duplicate.

Differential Scanning Calorimetry (DSC)

Prior to sample analysis, a baseline was obtained which was used as abackground. DSC analyses of terbutaline sulphate samples were carriedout on a Perkin Elmer 7 Series differential scanning calorimeter thermalanalysis system (Perkin Elmer Ltd., Beaconsfield, UK). Temperature andenthalpy were calibrated with the standard materials indium (meltingpoint=156.6° C.) and zinc (melting point=419.5° C.). Samples (1-10measurement range of the AeroSizer™ is nominally from 0.2 to 200 μm ofaerodynamic diameter with the standard 750 μm diameter tapered nozzle.The micronised and SEDS™ TBS samples

mg) were accurately weighed into pierced, crimped aluminium pans andheated at 10° C. min⁻¹ over a heating range of 25-290° C. under anitrogen purge. A chiller unit was used in conjunction with thecalorimeter to attain the lower temperatures.

Dynamic Vapour Sorption (DVS)

The moisture sorption isotherm of each powder at 25° C. was measuredusing a dynamic vapour sorption (DVS) instrument made by SurfaceMeasurement Systems, UK. This instrument gravimetrically measures uptakeand loss of water vapour on a substrate by means of a recordingmicrobalance with a resolution of ±0.1 μg. In the first step of theexperimental run, the sample was dried at 25° C. and 0% relativehumidity (RH) for at least 600 minutes to bring the sample to near zerowt % H₂O. Then, the instrument was programmed to increase the RH insteps of 5% RH from 0% to 90% RH and decrease the RH in steps of 10% RHfrom 90% to 0% RH. A criterion of dm/dt=0.005%/min was chosen for thesystem to hold at each RH step before proceeding to the next RH step.Sample masses between 30 and 100 mg were used in this study. The changein mass (%) is expressed in terms of g H₂O per 100 g of dry substance.

Isothermal Microcalorinietry

A Thermal Activity Monitor (TAM, model 2277; Thermometric A B, Jrflla,Sweden) was used to measure the calorimetric heat flow (μW) vs. % RHprofile of each sample. A RH-perfusion cell (Model 2255-120) accessoryfor the TAM was used to control RH within the sample vessel. The carriergas, dry N₂, was flowed at a constant rate (1.48 cm⁻³/min). Allexperiments were performed at 25° C. About 100 to 105 mg accuratelyweighed of each powder were placed in a stainless steel ampoule,attached to the RH perfusion cell, and then dried under 0% RH until astable heat flow signal was reached (e.g., a signal within the range of−1 to +1 μW). The RH was then increased in a linear ramp from 0 to 90%over the following 30 hours (i.e., 3% RH/hr). The heat flow arising frominteractions of water vapour with the solid sample was measured as afunction of time. Since RH changed with time in a linear fashion, theheat flow was also known as a function of RH.

The TAM measures the total heat flow in power, P, produced from either aphysical or chemical reaction. In this study the calorimetric power isproportional to the rate of moisture sorption or desorption,crystallization, and/or other processes. Exothermic events are measuredas a deflection in the positive y-axis direction. Althoughcrystallization is an exothermic process, it can be observed as a netendothermic process. During crystallization, there is an exotherm due tocrystallization and a simultaneous endotherm due to desorption ofpreviously sorbed moisture. The TAM profile gives the resultant of theseprocesses. Hence, for crystallization, the TAM profile can be anexothermic peak only, an endothermic peak only or a sequentialcombination of both exothermic and endothermic peaks.

Inverse Gas Chromatography (IGC)

An empty GC column was uniformly packed with the powder of interest(TBS). Pre-silanised commercially available straight glass columns of 30cm length with a 3 mm internal diameter were used in this investigation.The silanation procedure was necessary to minimize active sites on theinner glass surfaces, which strongly interact with polar probes. Eachcolumn was packed at the detector end with a small amount of silanisedglass wool, was clipped to a stand and powder was added through a glassfunnel with the aid of a mechanical column packer (tapping) to improvepowder flow and remove any air gaps. Once the column had been filled,the injector end of the column was also packed with silanised glass wooland attached to a separate, purpose built column oven that controls thesample (column) temperature between room temperature and 90° C. A.Hewlett Packard 6890 Series Gas Chromatograph (GC) (Hewlett Packard,Penna, USA) oven equipped with an autosampler was used to control thesolvent temperature. The 6890 GC data acquisition system was used torecord data from a thermal conductivity detector (TCD) and flameionisation detector (FID) with the instrument modified for IGC bySurface Measurement Systems (SMS), Manchester, UK. The combination ofdetectors allowed sensitive analysis of both organic vapour elution andwater (although RH was not raised above 0% for these experiments).

The whole system was fully automated by control software (SMS iGCController v1.3) and the data analysed using SMS iGC Analysis macros.Prior to analysis, each column was equilibrated at 30° C. and 0%relative humidity (RH) for 5 hours by passing dry helium gas through thecolumn. Helium gas was also used as the carrier gas. Hydrogen andcompressed air flow rates were set at 40 and 450 ml min respectively forthe FID. The chromatograph injection port was maintained at 80° C., TCDdetector at 150° C. and the FID detector at 150° C. Column temperaturewas set at 30° C. throughout analysis. Data were obtained by flowinghelium gas at 10 ml min⁻¹ the sinalised glass column packed with a knownweight of powdered material and injecting small amounts (concentrationP/Po=0.05) of a range of probe vapours with different polarities. Theretention times of the probes were measured using SMS iGC Controllerv1.3 software, at infinite dilution or near zero surface coverage(equivalent to 10⁻⁴-10⁻⁷ μl of liquid) where retention is independent ofthe quantity of probe injected. For each sample, two columns wereprepared and analysed by employing a method based on standard settings,which allows the precise control and measurement of experimentalvariables. This is essential in producing meaningful results. The datawere used to calculate the dispersive and non-dispersive forces actingat TBS particle surfaces using the method developed by Schultz andco-workers (J. Schultz, L. Lavielle and C. Martin. The role of theinterface in carbon fibre-epoxy composites, J. Adhesion, 23, 45-60(1987)).

Powder Analysis

Aeroflow Method

An Aeroflow™ powder avalanching apparatus (Amherst Process Instruments,API, Amherst, USA) was employed to analyse the dynamic avalanchingbehaviour of micronised and SC processed TBS samples. The Aeroflowapparatus consists of a transparent rotating drum with a port at thefront. A white light source is positioned in front of the drum and amasked array of photocells is behind the drum. To measure avalanching,50 ml of the drug powder was added to the drum, which is about 15% ofits total volume to ensure good powder mixing during the operation. Asthe drum rotates, the powder bed is carried upwards until an unstablestate is reached and an avalanche occurs.

The time between successive avalanches was recorded by the projection ofthe light beam through the drum onto the photocell array. The photocellsgenerated a voltage dependent on the amount of light falling on thecells and the area of unmasked photocells shielded from the light sourceby the powder. The voltage output (transmitted light intensity) wasrecorded by a computer, which translates the output as powder movementusing a technique disclosed in B. H. Kaye. Characterising theflowability of a powder using the concepts of fractal geometry and chaostheory, Part. Part. Charact. 14: 53-66 (1997). Each TBS sample wastested in duplicate and mean avalanche time and irregularity (scatter)of avalanches were recorded.

Powder Dispersion by Cascade Impaction

An Andersen Cascade Impactor (1 ACFM Eight Stage Non Viable AndersenCascade Impactor, Copley Ltd, Nottingham, UK) was used to determine thedispersability and fine particle fraction (FPF) of each powder/carrierblend and pure drug alone through a dry powder inhaler device(Clickhaler®, Innovata Biomed, St. Albans, UK). To prevent particlesfrom bouncing off the plates and becoming re-entrained in the air streamprior to each analysis, the eight metal plates of the impactor werecoated with a thin layer of silicone spray and left to dry for 30minutes. A pre-separator was attached to the top of the impactor toprevent large particles or aggregates from reaching the stages. The airflow through the apparatus, measured at the inlet to the throat, wasadjusted to generate a pressure drop of 4 kPa over the inhaler undertest and a duration consistent with the flow of 4 liters min⁻¹ accordingto compendial guidelines (Pharm Forum, 22: 3049-3095 (1996). Theseconditions are consistent with a flow rate of 49 1 min⁻¹ and 4.9 sduration. A blend containing 3.8% w/w of compound, hand-filled into thereservoir of a Clickhaler® device, which is capable of delivering 200 μgof drug per actuation, was used. Ten doses were discharged into theapparatus and each determination was carried out at least twice. Aftereach determination, the powder on each impaction stage was collected byrinsing with mobile phase and the resulting solutions were analysed byHPLC. The amount of drug deposited in the throat piece and thepre-separator was also determined.

The Andersen cascade impactor is traditionally calibrated at 28.3 1min⁻¹ but may be operated at higher flow rates, which are thought tomore closely approximate a patient's capabilities (F. Podczeck.Optimisation of the operation conditions of an Andersen-Cascade impactorand the relationship to centrifugal adhesion measurements to aid thedevelopment of dry powder inhalations, Int. J. Pharm., 149: 51-61(1997)). Using a variation of the Stokes' equation, effective cut-offdiameters (ECDs) at the higher flow rate can be calculated from theequation given below (M. M. Van Oort, B. Downey, and W. Roberts.Verification of operating the Andersen Cascade Impactor at differentflow rates, Pharm. Forum, 22: 2211-2215 (1996).ECD_(F2)=ECD₂₈ ₃(28.3/F2)^(1/2)

where ECD_(F2) is the ECD at the alternative flow rate, ECD_(28.3) isthe manufacturer's flow rate (28.3 1 min⁻¹) and F2 is the alternativeflow rate in 1 min⁻¹. The alternative flow rate used in this study was49 1 min⁻¹. Particles collected on the filter were smaller than 0.32 μm.The percentage of the total dose collected on the stages 1 through 5represented particles with the aerodynamic diameters less than 4.36 μm,and was considered as the fine particle fraction (FPF).

Results and Discussion

Powder Preparation and Optimisation

TBS was produced using the SEDS™ process. Different solvents such aspure methanol, methanol/water, pure water and pure ethanol were used todissolve drug material between 1-10% w/v in concentration. To optimisethe particle properties (crystallinity, shape, size, size distribution)a number of parameters such as concentration of the drug, drug solutionflow rate, CO₂ flow rate, temperature and pressure of the system weremanipulated. A wide range of SEDS™ products such as a hydrated crystal,amorphous material, and two previously reported polymorphs A and B wereproduced using different solvents and experimental conditions. Forexample, the clear difference in morphology and crystallinity(determined by XRPD which was based on diffraction peaks area and DSC bymeasuring change in enthalpy of fusion) of TBS1 (127.12 J/g) and TBS2(88.68 J/g) may be attributed primarily to the different residence timefor particle formation and mixing in vessels which is defined as τ=V/f,where V is the volume of the vessel and f is the volumetric flow ratesof ethanol and CO₂ at given temperature and pressure respectively.Particles in the smaller 50 ml vessel were exposed to partially mixedethanol-rich phase which exist in the core of high velocity jet (B. Y.Shekunov, J. Baldyga, and P. York. Particle formation by mixing withsupercritical antisolvent at high Reynolds numbers, Chem. Eng. Sci., 56:2421-2433 (2001)), whereas the particles in the large 500 ml vessel wereaccumulated in well mixed CO₂-rich phase.

SEM photomicrographs of a typical micronised and SCF processed batchesof TBS were obtained. The use of different solvents such as puremethanol and methanol/water resulted in needle-like as well as-sphericalamorphous particles respectively. Particles obtained using puremethanol, pure ethanol and pure water have revealed well-defined crystaledges compared to micronised particles.

Particle Size

The average particle size by volume determined by laser diffraction fora typical batch of TBS1 and TBS2 was between 3.2 and 3.4 μm with 90%less than 7 μm in comparison to 3.0 μm microparticles of micronisedterbutaline sulphate with 90% less than 5 μm. This method showed goodreproducibility and therefore, was used for the quality controlassessment.

The samples were also analysed with the AeroSize™. Micronised, TBS1 andTBS2 samples have similar aerodynamic diameters to those obtained by theSympatec™ laser diffraction instrument. However, TBS3, TBS4 and TBS5showed larger mean diameters by AeroSizer™ in comparison to laserdiffraction analysis. These results are depicted in Table 7 below. TheAeroSizer™ gives an aerodynamic equivalent diameter, which is smallerthan geometric volume diameter for non-spherical primary particles.Therefore, the results here likely indicate insufficient dispersion byAeroDisperser™ of the agglomerated particles of both batches TBS4 andTBS5. In addition, the sampling procedures in the AeroSizer™ nozzle mayproduce discrepancies in time-of-flight measurements at large particlenumber densities, which is the case of small amorphous particles inTBS4. Therefore, the reproducibility of results for this technique waslower than for the laser diffraction method.

TABLE 7 Sample Sympatec D_(4,3) (μm) Aerosizer D_(4,3) (μm) Micronised3.04 2.69 TBS 1 3.22 3.31 TBS 2 3.43 3.44 TBS 3 1.99 6.69 TBS 4 4.7515.53 TBS 5 4.84 11.44

X-Ray Diffraction and DSC Profiles

The X-ray powder patterns in FIGS. 5A-5C illustrate the crystallinity ofmicronised and TBS1 and TBS2 samples, which is assessed on the basis ofthe sharpness of the major diffraction peaks. From the results it can beseen that there is no significant difference in the XRPD profiles ofmicronised and TBS1 samples. However, based on XRPD data, the TBS2sample has shown lower bulk crystallinity in comparison to themicronised sample. The DSC profiles (Table 8) confirm this conclusion;the fusion enthalpy for TBS2 batch is considerably lower than for bothmicronised and TBS1 batches, thus the crystallinity for TBS1 beinghigher than that for the micronised material.

TABLE 8 Enthalpy of Fusion Sample Melting Point (° C.) (J/g)Identification Micronised 266.3 121.76 Form B TBS 1 267.1 127.12 Form BTBS 2 266.3 88.68 Form B TBS 3 266.3 31.35 Amorphous TBS 4 274.5 40.98Hydrate TBS 5 272.7 57.69 Form A

Interactions of Water with Micronised and SEDS™ Powders

The sorption and desorption isotherms of micronised and SC processed TBSshow that at 25° C., the equilibrium moisture content (“moistureuptake”) of all TBS samples in this study is very low (<0.4%) at any RHvalue. The low moisture uptake indicates that each powder iscrystalline. However, TBS2 sample showed slightly higher moisture uptakethan the micronised sample, which is consistent with its lower bulkcrystallinity indicated by DSC and X-ray diffraction (see FIGS. 5A-5Cand Table 8). Typically, an amorphous or partially crystalline materialwill take up more moisture than a highly crystalline material. TBS2 alsotakes up more moisture at relative humidities beyond 90% RH. Under theseconditions, the sample may be deliquescing at high RH.

In FIG. 6, the heat flow (μW) for both micronised and SEDS™ powders ofTBS are normalised to 1 mg for comparison. The endothermic peak formicronised TBS is most likely due to crystallisation of the amorphousfraction that was previously induced by micronisation. The TAM profilefor TBS2 sample of TBS has an incomplete exothermic peak between 85 and90% RH because the RH ramping experiment (3% RH/hr from 0% to 90% RH)ended before the event was completed. No exothermic or endothermic peakswere observed in the TAM profile of TBS1 sample of TBS, which is typicalfor a highly crystalline material. The TAM results show that themicronised TBS has an event at about 79% RH, probably due tocrystallisation. The results also show that TBS2 sample has anexothermic event at about 85% RH.

Surface Energetics Properties

Micronised and supercritically processed TBS1 materials show verysimilar surface energetics with marginally lower non-polar, dispersivesurface interaction (γ_(S) ^(d)) and slightly higher specificinteraction (−ΔG_(A) ^(SP)) for polar, amphoteric and basic probes. Incontrast, the TBS2 sample indicated significantly less energetic, bothdispersive and specific, interactions (Table 9). In addition, comparisonof the K_(A) and K_(D) values of TBS2 and micronised samples (Table 10)indicates the weakest, both acidic and basic interactions for thissupercritically processed material. Thus, the SEDS™ material has lessexposed energetic acidic and basic groups. This also indicates that thesurface of TBS2 particles may have a more ordered structure than thatfor micronised material, despite the fact that the bulk structuredetermined using X-ray diffraction and DSC techniques appeared moreordered for the micronised particles. Micronised material is sometimesconditioned before being used for a DPI formulation, by passing asaturated ethanol vapour through the powder bed. Similarly, TBS1material was produced with an excess of ethanol solvent. Therefore, itis possible that the surface structure was modified after particleformation for micronised and TBS1 materials and disorganised compared tothe crystal structure in the bulk.

TABLE 9 −ΔG_(A) ^(SP) (kJ/mol) Ethyl Chloro- Sample γ_(s) ^(D) mJm⁻²Toluene Acetone acetate form Dioxane Micron- 58.61 3.42 12.57 16.01 1.7915.96 ised TBS 1 57.37 3.66 13.41 16.65 1.68 — TBS 2 55.05 2.85 10.4213.76 1.21 14.20

TABLE 10 Sample K_(A) K_(D) Micronised 0.892 0.051 TBS 1 0.761 0.020 TBS2 0.778 0.032

Powder Flow Properties

For data obtained using the Aeroflow™ powder avalanching analyser,interval times between avalanches were plotted as discrete phase mapsknown as strange attractor plots (B. H. Kaye, J. Gratton-Liimatainen,and N. Faddis. Studying the avalanching behaviour of a powder in arotating disc, Part. Part. Charact. 12:197-201(1995). Free-flowingpowders produce strange attractor plots close to the origin with smallspread, whilst, in contrast, cohesive powders give plots with a largerspread and a centroid positioned further from the origin. The strangeattractor plots for TBS analysed at high (100 seconds per revolution)and medium (145 seconds per revolution) rotation speed are shown inFIGS. 7A-7B and 8A-8B, respectively.

Examination of the strange attractor plots provides a clear, visualdisplay of the difference in flow behaviour between the micronised andTBS2. The SEDS™ sample has a lower irregularity and a lower meanavalanche time (see Table 11 and FIGS. 7A-7B and 8A-8B) compared tomicronised TBS. Therefore, micronised TBS exhibits poorer flow behaviourthan TBS2 material. Since a relatively large quantity (≈10 g) of powderis required to perform powder flow behaviour study, no comparison wasmade between TBS1 and micronised samples.

TABLE 11 Mean time to Sample avalanche (s) Irregularity of flow (s)Micronised (100 sec/rev) 3.62 1.28 Micronised (145 sec/rev) 5.72 2.39TBS 2 (100 sec/rev) 3.30 1.17 TBS 2 (145 sec/rev) 4.91 2.12

Enhanced flow properties of TBS2 sample are consistent with lowerenergetics and lower cohesiveness of this material as indicated by theIGC measurements and the following ACI studies.

Aerosol Performance of Micronised Vs SEDS™ Powders

FIGS. 9 and 10 compare the in vitro performance of micronised and SEDS™processed TBS analysed in a lactose blend as well as pure drug alone.The ACI measurements demonstrated that the TBS2 batch in both casesproduced a significantly higher FPF in comparison to both micronised andTBS1 material. For this material, a high proportion of fine particlemass with a narrow distribution was collected on stage 1-3 in contrastto the broad distribution across stages 1-5 for the micronised material.The SC processed TBS2 material also demonstrated an increased fineparticle fraction (FPF) in both lactose blend and drug alone compared tomicronised powders (38.6% vs 30.7%, and 29.6% vs 17.7%) and increasedemitted dose (see Table 12). Since the lactose particles are large andcannot penetrate beyond the pre-separator stage, this indicates thatdispersion between pure drug particles and formation of loose aggregatesplays a major role in defining the deposition profile.

TABLE 12 Total Emitted Dose (mg/dose) Fine Particle Fraction (%) Drugand Drug and Drug Sample Lactose Blend Drug Alone Lactose Blend AloneMicronised 80.6 84.2 30.7 17.7 TBS 1 71.6 83.7 11.4 9.4 TBS 2 104.8 98.838.6 29.6

The main factor responsible for better performance of supercriticallyprocessed TBS powder in the ACI is possibly related to thedispersibility of this powder at low air flow rates. The enhanceddispersibility is particularly significant for DPI devices where theperformance strongly depends on powder deaggregation at relatively lowdispersion forces. Clearly, high turbulence is favourable for dispersionbut it inevitably leads to high pressure differentials which may beunacceptable for correct functioning of many devices.

Example 10

The example assessed the force of adhesion of particles of salbutamolsulphate produced using a SEDS™ processes compared to the same compoundin micronised form. Conventional AFM analysis was used. Particles of thesamples were mounted onto AFM probes and the adhesion force per unitarea to a freshly cleaved highly oriented pyrolytic graphite substrate(HOP G, Agar Scientific, Essex, UK) in a liquid (2H 3H perfluoropentane)environment was determined. The contact area involved in the interactionwas assessed and related to the force measurements.

The initial forces for individual particles of the micronised and SEDS™produced materials were 15.77 nN (SD 4.55 nN) and 4.21 nN (SD 0.71 nN)respectively.

Following correction for surface area, the forces per unit area were100.91 nN/μm² (SD 29.15 nN/μm²) for the micronised material and 13.52nN/μm² (SD 2.27 nN/μm²) for the non-micronised SEDS™ process producedmaterial. The particulate product of the invention clearly demonstrateslower adhesiveness than the micronised version of the same substance.

Example 11

The aerosol performance of a SEDS™ processed sample of bromocriptinemesylate was assessed in a unit-dose passive inhaler device (TurbospinPH & T (Italy)), at a peak inspiratory flow rate (PFIR) of 28.3 LPM and60 LPM.

TABLE 13 Emitted dose performance with relative standard deviations ofSEDS bromocriptine using Turbospin. Errors correspond to RSDs. Fill FlowWeight Rate ED Left in Capsules (mg) (LPM) (%) (%) 8.0 28.3  67.7 ± 14.710.5 ± 118  60 87.5 ± 3.4  −0.1 ± −2320 4.0 28.3 75.4 ± 3.9 −1.5 ± −13460 83.8 ± 4.0 0.5 ± 347

The aerosol analysis (performed @ 60 LPM) indicated that bromocriptineyielded aerosol particles within respirable range with an aerodynamicdiameter of 4.2/μm (4.3% RSD) and an improved FPF (42% of ED).

Bromocriptine dispersed well at high flow rates (ED>80%) regardless offull weight. Moreover, it exhibited minimal flow rate defendence, as EDdrops were minimal (8-20%) following emptying of the capsules.

The invention claimed is:
 1. A method of administering an activesubstance by inhalation, the method comprising delivering the activesubstance by oral inhalation via an inhaler, wherein the activesubstance is in particulate form, the particulates having: a) a volumemean aerodynamic diameter of less than 7 microns; b) a bulk powderdensity within a range from about 0.1 g/cm³ to about 0.5 g/cm³; and c) asurface-to-volume ratio of at least 2.5 that of spherical particles of acorresponding volume diameter, and wherein the particulates are solid,non-hollow, non-porous particles.
 2. The method of claim 1, wherein theactive substance further comprises a shape factor of at least
 2. 3. Themethod of claim 1, wherein the active substance further comprises ashape coefficient of greater than
 10. 4. The method of claim 1, whereinthe active substance further comprises an aerodynamic shape factor of atleast 1.4.
 5. The method of claim 1, wherein the active substancefurther comprises a specific surface area of at least 10 m²/g.
 6. Themethod of claim 1, wherein the active substance further comprises aspecific surface area of at least 15 m²/g.
 7. The method of claim 1,wherein the active substance further comprises a specific surface areaof at least 20 m²/g.
 8. The method of claim 1, wherein the activesubstance further comprises a specific surface area of at least 25 m²/g.9. The method of claim 1, wherein the active substance further comprisesa volume mean diameter of less than 6 microns.
 10. The method of claim1, wherein the active substance further comprises a specific surfaceenergy of less than 100 mJ/m².
 11. The method of claim 1, wherein theactive substance further comprising a specific surface energy of lessthan 70 mJ/m².
 12. The method of claim 1, wherein the active substancefurther comprises a RMS roughness, measured using AFM, of 0.5 nm orless.
 13. The method of claim 1, wherein the active substance furthercomprises a particle size distribution (X₉₀) within a range from 0.5 μmto 10 μm.
 14. The method of claim 1, wherein the active substancefurther comprises an amorphous phase content of less than 1% w/w. 15.The method of claim 1, wherein the active substance further comprises abulk powder density of 0.2 g/cm³ or less.
 16. The method of claim 1,wherein the active substance further comprises a shape factor of atleast 3.5.
 17. The method of claim 1, wherein the active substancefurther comprises a RMS roughness, measured using atomic forcemicroscopy, of 0.2 nm or less.
 18. The method of claim 1, wherein theactive substance, which when delivered using a passive dry powderinhaler, yields a fine particle fraction in the emitted dose of 20% orgreater.
 19. The method of claim 18, wherein the active substance yieldsa fine particle fraction in the emitted dose of 31% or greater.
 20. Themethod of claim 18, wherein the active substance yields a fine particlefraction in the emitted dose of 55% or greater.
 21. The method of claim1, wherein the active substance is selected from the group consisting ofsalbutamol, terbutalene, salmeterol, fenoterol, bromocriptine or apharmaceutically acceptable salt or mixture thereof.
 22. The method ofclaim 1, wherein the inhaler is a passive dry powder inhaler.